[HTC One M8 for Windows] Gurm:
How to upgrade to Windows 10 on your HTC One M8 for Windows running Windows Phone 8.1

Prerequisites:

a.	A Microsoft account. You NEED one to do this. Preferably sync it with your phone BEFORE you do all this, it will make your life so much easier. Even if you are paranoid about Microsoft getting all your data, you STILL need an account to complete the steps here.

b.	Several pieces of software. Please use the versions specified in this walkthrough. Other versions have not worked well. You can download them all in a RAR file from: https://mega.nz/#!2JNBTCiZ!tBFDPMFzUu3g7EqulH9BSlFFebv4IcZiPrRSvS_fx88

c.	Patience. If you mess up a step, all the way up through the Windows 10 install, you can flash back to stock WP8.1! You can probably even downgrade afterwards.

d.	A MicroSD card is required. I didn’t have one installed on the phone before I started, but it’s 100% necessary (I’ll detail why as we proceed).

e.	A willingness to completely wipe your phone. This ought to go without saying, but I’ve had people ask me “oh you mean I have to delete EVERYTHING?” Yes. Your phone will be reset to factory at least once in this process.

Credits:

Thanks to Bladeni, on whose instructions this is based. And all the folks at XDA Developers and Betanews, Disqus and a few other places I’m probably forgetting. The guys who wrote WindowsPhoneCustomPFD and CustomWPSystem. And the whole community!

Walkthrough:

1.	Backup all your data. Preferably to the cloud. But if you are a privacy nut, put it all on your computer. Or the SD card. Somewhere other than main phone RAM which is going to be completely wiped.

2.	Charge your phone to 50%. I know other walkthroughs say 40, and the tools say 25, but the reality is that we don’t know how fast your battery will drain once the phone is in bootloader mode.

3.	If for some reason you have Windows Insider or Preview for Developers installed, uninstall them now!

4.	Install the Windows Device Recovery Tool on your PC and run it.

5.	You may also at this point want to install HTC Sync Manager, just to get the HTC drivers.

6.	Restart in bootloader. This is a point of some contention, but basically hold down the power button until the phone tells you to swipe to restart. As soon as the screen goes black, hold down both volume buttons. You should get this screen (those are barcodes under the black swatches):

a.	If the phone shuts all the way down, just hit the power button for a long press, then immediately hit the volume buttons. It takes a couple tries if you’ve never done it.

7.	Plug the cable into the phone and the computer. Wait for Windows to recognize the device. Check Device manager to make sure it shows up as HTC Phone and not an unknown device.

a.	If it shows up as an unknown device, try installing HTC Sync Manager (see list at end).

b.	If it STILL shows up as unknown, install HTC Drivers Standalone (see list).

c.	If that doesn’t work, as a last resort, right click the unknown device, update driver, and browse to where you unzipped the Fujitsu driver.

8.	Once the device is recognized, you may need to hit “My device was not detected” in the Recovery Tool.

a.	If you do, browse to “Other OEM’s” and then to “HTC”.

9.	Now hit next, don’t give a reason (“Continue without submission”), and wait. After a few minutes, your phone will be back to Windows 8.1 factory image.

10.	You need to set up WP8.1 – sign in with your account. If it starts to restore your stuff, let it do so – you have to wait until the queue is clear before you can proceed, so take this time to install the other software you need:

11.	Install the WP8.0 SDK Tools Lite Setup. It may give errors about setting up links. Ignore them.

12.	Install the WP8.1 SDK Tools Lite Setup. It may give errors also but usually won’t.

13.	Once the phone is stable, go to Storage Sense and make sure that apps are set to install TO THE PHONE. This is super important!

14.	If for some reason you still have Windows Insider or Preview for Developers installed (you shouldn’t, after step 2), uninstall them now! I’ve seen this happen with Preview for Developers.

15.	Under the Windows Phone SDK 8.1 on your PC (NOT THE 8.0!) run “Windows Phone Developer Registration”.

a.	Unlock the phone, it HAS to be on the start screen for this to work.

b.	Log in with your Windows account (same as on the phone! Very important!) and hit “register”. You can tell it worked because when you run it again, it will say “unregister” (don’t unregister, but you can check!)

16.	Under the Windows Phone SDK 8.1 on your PC, run “App Deployment” and select the CustomWPSystem_0500.xap file you previously downloaded. Deploy it.

17.	Now open up your phone in explorer, and go to the downloads folder. Drag the CustomPFD_0003.xap into this folder. DO NOT DEPLOY THIS XAP.

18.	If you want HTC Sense TV, download it from the store now, since after this step it will be impossible to install.

You are now ready to start modding the phone. Nothing you’ve done until this point has been destructive or done anything other than a reset. Now is the point where you probably void your warranty. You’ve been warned! We are about to hack a Microsoft app to make it into a registry editor.

19.	THIS IS CRITICAL. Navigate to storage sense and set apps to install to the SD card. If you don’t do this, NOTHING ELSE WILL WORK FROM HERE ON OUT.

20.	This website has a helpful set of screenshots for the next section: http://windowsphonecustompfd.blogspot.com/2015/01/you-need-two-filesfirst-custompfd0003.html?m=1

21.	Download the “Preview for Developers” app from the store. Wait for it to finish installing.

22.	Run the CustomWPSystem app on your phone.

23.	Tap the red button labeled “SD Card Permissions”, then tap SD Card, then hit the check mark. The button should turn green.

24.	Make sure “Preview for Developers” is selected (it is the default).

25.	Now select the CustomPFD_0003.xap file using the select button.

26.	Hit “apply XAP”. IF THE APP CRASHES AT THIS POINT, you have done something wrong. Most likely you didn’t set apps to download to the phone and SD card at the right places. The CustomWPSystem app MUST be installed on the phone and the Preview for Developers app MUST be installed to the SD card. You MUST be logged in with the correct Windows account. Go back and check everything again. If you have to, drop back to the system restore again using the Recovery Tool.

27.	Go to the apps pane, and you should see that Preview for Developers now has a weird green icon with a key on it instead of the purple icon it came with. If it doesn’t, see step 25.

OK, for real. Now you’re going to void the warranty, since you’re about to edit the registry. Basically we are about to trick the phone into thinking that it’s a Nokia Lumia 735, which is a phone with roughly similar specs to this one, at least as far as the Windows 10 update process is concerned.

28.	Run the Preview for Developers. This is now a modifier registry editor. You’ll see “cannot write here”. That’s normal. Navigate to:

a.	HKLM (HKEY_LOCAL_MACHINE)

b.	SYSTEM

c.	Platform

d.	DeviceTargetingInfo

29.	Now you’ll see you can write. So let’s find the keys we need. There are three. In each case, pick the key, then you’ll do this:

a.	Hit the plus at the bottom.

b.	Put the name of the key in the top field.

c.	Pick “String” instead of “Key”.

d.	Put the required data in the bottom field.

e.	Hit “write”.

30.	If your screen doesn’t move the keyboard out of the way, just hit back (ONLY ONCE) to get the other fields to show.

31.	The three keys, with their data, are as follows. Remember they should all be set to type “string”:

a.	PhoneManufacturer (yes, caps are important and leave off the quotes) is currently “HTC”, change it to “NOKIA”.

b.	PhoneManufacturerModelName is currenly “HTC6995LVW”, change it to “RM-1089_1087”.

c.	PhoneModelName is currenly “HTC6995LVW”, change it to “Lumia 735”.

32.	Double check them by clicking back into them one at a time. Make sure the data is correct.

33.	Download the “Windows Insider App” from the app store, and run it.

34.	Register, and click “get insider builds”. When presented with a choice, choose the top selection. This is called the “Fast Ring”. It gets you the latest preview build, which is needed for bug fixes for the HTC One M8. Prior builds – stable and prod – don’t have the keyboard or SIM card working properly.

35.	Reboot.

36.	After reboot, check for updates the normal way. You should see an update starting. This is Windows 10. Let it install. THIS TAKES A LONG TIME.

37.	Once you’ve rebooted into Windows 10, there will be a lot of other updates. Be patient and eventually it will be time to proceed.

38.	Go to your app pane – notice that the Insider app as well as the Preview app are all the way at the top under “recently added”. The Preview app has no text, just an icon. This is normal.

39.	Run the Preview app, and reverse the steps above to restore the original values (HTC, HTC6995LVW, HTC6995LVW) to the keys in steps 29-31.

a.	If your Preview app is missing, you can try the Interop tools (included here) but they crash on a lot of builds for a lot of people when you try to go into the “Platform” subkey of the registry.

b.	To install Interop tools, just load the file onto your phone and go run it from file explorer.

c.	To run Interop tools (it isn’t an app, it’s a control panel applet!), go to settings->extras->interop tools.

40.	Run the Insider app again, and this time put it onto release ring (the bottom option). This is optional – you can choose to continue to get all the latest options, but the latest ones tend to be buggier. I will update these instructions when the release build is good enough for the HTC One m8 to use in step 34. But for now, you may want to do this step.

Again, the download location is:

https://mega.nz/#!2JNBTCiZ!tBFDPMFzUu3g7EqulH9BSlFFebv4IcZiPrRSvS_fx88