Disclaimer: As with all software/system updates, run a backup prior to changing anything!  Don’t blame me if you screw something up!   🙂

This method will probably work for a lot of HTC phones, certainly in the Desire line.  I have an HTC Desire 626s (Metro PCS) that I use exclusively for my quadcopter.  The fact that it only has 8gb of storage?  Well we won’t talk about that just know that it was free!  The steps outlined below work and work well for updating it, I’ve used them to go from Lollipop to Marshmallow and then also to update Marshmallow.  I’m shocked that HTC is still pumping out updates for this beast!

Both times I spent over an hour searching Google, XDA and other sites.  So I’m creating the post to make it easier for me to remember how to do it once, per year as well as for other people to find it an use it.

Originally I pulled the OTA’s (with Root Browser) to a Windows PC and removed the recovery as I didn’t want to lose TWRP.  That didn’t work because then the update was signed and the phone will not flash an unsigned zip file.  Going down the “S-Off” rabbit hole was another hour of wasted time that I didn’t need to go down.  In the end I decided against it and it seems either difficult or expensive.

The original post is below but here is how I did it.

1. Download the RUU (Rom Update Utility) from HTC for your phone from here: http://www.htc.com/us/support/rom-downloads.html
2. “Run” the update, allow it if you have UAC enabled, when it asks for you to agree to continue don’t hit anything.
3. With the installer sitting on the EULA screen, hit the “Windows+R” to bring up the run command and type %temp% and hit enter.
4. In this folder, do a search in the top right for rom.zip and copy it to the microSD card you are using for the phone.
5. Once on the microSD card, rename it exactly to this file name: 0PM9IMG.zip
6. Reboot, when prompted to run the update go ahead and do it.  It will take a while and reboot numerous times.
7. Once completed and you are back up and running, rename or delete the file so it won’t keep trying to run at every reboot.  Also, it will re-run regardless at reboot as I found out the hard way.

I’ll post some pictures down below the XDA quote so you can see what screens to expect.  Like I said it will reboot multiple times and flash through a bunch of scary black screens with red letters.

Flashing without RUU

First, download the RUU and run the .exe up until it prompts you to begin the install to the phone. Don’t do that.

Go to Windows Explorer and in the address bar put “%temp%” and find “rom.zip”

Rename it “0PM9IMG.zip” and put it in the root directory of your external SD and from here you can do whatever you want. I used the bootloader to install it rather than TWRP.