[Honor 8 Guides, News, & Discussion] sic0048:
EDIT - this post made me go ahead and create a new Guide thread. Please check it out if you are wondering how to take an upgrade if you have unlocked and rooted your phone.

Here is the original post I made....

I just researched this myself and this is what I did....

1) Make a backup using TWRP (if the new update locks the phone, you will need this backup to restore data after unlocking it)

2) The update won't work with TWRP as your recovery, so we need to flash the original Huawei recovery to replace TWRP. If you are like me, you don't have a copy of the stock recovery image on hand (if you do have a copy, then skip to step 3). Therefore we need to extract it from the stock ROM image. Download the stock ROM image for your device. This website seems to have a list of recent versions and it is where I downloaded the L14 B389 version that I used.

download the Hauwei Update Extractor software and install it on a computer. Here is a Youtube video showing how to use it. You only need to extract the "Recovery.img" file for our use (the video extracts several additional files that we don't need). Move the stock recovery image to your ADB folder so you can flash it in step 3.

3) Use the stock recovery file and flash it to recovery using the same instructions as you used to flash TWRP in the first place. If you need a refresher, look at section 2 of the first post in this thread. Just make sure you substite the name of the stock recovery image instead of TWRP.

4) Reboot into system

5) Go to the Settings - System Update menu on your phone. In the upper right corner, click on the three dots and it will bring up a menu where you can choose "Download latest full update". Click on this. This will start the update process by downloading the full ROM and not just the smaller update package. For me the package size was approaching 3gb, so make sure you are ready to handle that size transfer. For me, the phone automatically did the update after downloading the package. I was nervous at first, but everything went fine. If for some reason the update fails, I would reboot and try again. I did have one failure, but I cannot explain if it was a bad download, or something I did wrong. It worked fine the second attempt.

6) The phone will reboot and you should check the status to make sure you are on the latest version.

7) I read where people said full updates would lock your phone and you would have to start from scratch unlocking it (and therefore wiping all data). This was not the case for me and this update. I was simple able to flash TWRP again. You should be a rock star at flashing recoveries by now so get to it and flash TWRP again. If your phone is locked, the read the note at the bottom of this post.

8) Reboot into system

9) Reboot into recovery and flash Magik zip to get SuperSU.

10) Reboot into system. Reinstall any Magik modules you use as they don't get carried over from the previous installation.

11) Enjoy your updated phone

If for some reason the full update did lock the phone, then you will need to unlock it again before you can flash TWRP. You have already done this before, so use whatever method was successful for you. Obviously this will fully wipe your phone. After flashing TWRP and Magik, I would make a backup of that raw "stock" image just in case this next step doesn't work. After making the backup, you can try to restore just the data partition of the NAIDroid backup you made in step 1 (click restore in TWRP, select the backup made in step 1 but deselect everything except the "data" partition before starting the restore process.) I have never done this, but I have read it will recover all your data (apps, etc) without affecting the system partition and therefore it won't mess up the upgrade. I would not recommend doing this if going from Marshmallow to Nugget or Nugget to Oreo however. In those cases, it is better to simple start fresh and redownload all of your apps.