[Xperia Z2 General] norti:
With the latest firmwares not directly rootable you need to download or create an update package with root and recovery and update your system via recovery. This won't delete your data and root will be there on 5.x.x. I made this complete tutorial so that everyone can make an update from an FTF file.

THIS IS FOR

LOCKED

BOOTLOADER and/or STOCK KERNEL ONLY !!!

MAKE SURE YOU HAVE A BACKUP !!!​

1.1 You need obviously an already rooted phone with [NUT]'s DualRecovery installed and working (this can be achieved on firmwares with Android 4.4 and 5.0.2)

If you don't have the recovery, you can install it from here: [Z2][TWRP][PhilZ Touch][CWM] XZDualRecovery Q&A see post #2 there for instructions. 2.8.12 and later should work on KitKat and Lollipop too!

1.2 You need Flashtool with working USB drivers (Make sure flashmode works - which means the drivers are properly installed on your system, especially on Windows 8/8.1/10 - before you start this tutorial).

2. Download the newest FTF update file for your phone/branding. Use the same customization version (xxxx-xxxx) that is on your phone now!

This you can do with Flashtool (Devices/Check Updates menu) or download it from the [FTF] STOCK FIRMWARES for Xperia Z2 thread.

(Alternative option for advanced users: XperiFirm -> you can create an FTF from the downloaded firmware files with Flashtool.)

3.1 Download PRFCreator v1.1.zip from [TOOL] PRFCreator - easily create pre-rooted firmwares.

3.2 Download latest stable SuperSU update package from here.

3.3 Download XZDualRecovery's latest - 2.8.23 -

flashable

version (Z2-lockeddualrecovery2.8.xx-RELEASE.combined.zip) from here (XZDualRecovery section).

You will have 5 files so far:

4. Unzip PRFCreator and run it.

5. Load the FTF, SuperSU and Z2-lockeddualrecovery (

flashable

) zip files into the three section.

6. Uncheck all the Include options [ ], we don't need them, we will flash them with Flashtool after the update. I think it's still safer to flash kernel, baseband, boot and other system critical parts of the firmware from Flashtool.

(But if you want to include them anyway then you can skip part 11 and start your phone normally.)

There is a Legacy mode option in the latest version. Without it PRFCreator will use a direct sin flashing method for system update. If you check the legacy option it will use the older repack method for system. The direct sin flashing should work in most cases if not then use the legacy option.

7. Push Create. After it's finished (wait for the Create button to be available again), you'll find a flashable.zip in the folder of PRFCreator.

Check the contents of the zip file, it should look like this with PRFCreator v0.5:

data
META-INF
system
utils
partition-image.sin
system.sin
dualrecovery.zip
SuperSU.zip

If something is missing, redo the process from step #4 until all is there.

8. Copy flashable.zip to the internal/external SD card of your phone. If you want to go for 100% working root and recovery copy UPDATE-SuperSU-v2.46.zip and Z2-lockeddualrecovery2.8.x-RELEASE.flashable.zip there too.

9. Boot your phone into recovery (use TWRP!).

10. Install flashable.zip in recovery. After finished DO NOT REBOOT !!!

*Optional step: install SuperSU and Recovery again so if something went wrong during the system flashing you'll still have a working recovery.

Clear Cache/Dalvik only and go back to Home and choose Reboot/Power off.

11. Start Flashtool and with the Flash device icon flash the kernel and other baseband files from the FTF in Flashmode.

Use the following configuration (or similar):

Wipe:

[ ] APPSLOG
[ ] CACHE
[ ] DATA

Which means nothing is wiped, this is good for a system update only, that reserves your settings, applications and data. (If you want a clean system or run into errors after updating only the system, you can wipe all the three.)

Exclude:

[ ] BOOTBUNDLE
[x] PARTITION
[ ] KERNEL
[ ] FOTA
[ ] BASEBAND
[x] SYSTEM
[ ] ELABEL

Which means system, partition and ta options are unchanged and won't be wiped/overwritten. You can exclude fota, elabel and baseband too, but some phone functions may be limited. Always use your phone's original customization version when choosing FTFs.

Never exclude = never check (x) kernel.

It is the main reason we're flashing this.

TA -> not always present in the FTF file, but if you see it, then EXCLUDE it, just to be sure, you don't simlock your device

[x] No final verification
[ ] Reset customization

Connect the micro USB to your phone and get ready with the other end of the cable in your hand :D

Push Flash button.

Push the Volume down button and connect the USB cable to the computer's USB port. Wait until Flashtool begins with the flashing and you can release the Volume button now.

When finished, unplug the the phone, start it and wait until it completes the first boot. After it is fully working, check SuperSU and if you can mount system R/W too (in Root Explorer or in other root file manager).

ENJOY another rooted version of Android ;) I can give support only for this process, for the tools you need to ask your questions in the appropriate threads above.

Thanks to [MENTION=3975929]zxz0O0[/MENTION] for creating the PRFCreator and the Lollipop fixes, it makes things easier in this process (you don't need to mess with linux mounts, virtual machines and other scripts copying system images and recovery updates to a zip).