Hey folks - this was posted by Brandon_T_R in another thread here. I just did this to my phone and it worked great. Hope this helps some folks out.
Anyway, here are the steps (in English ) to do the upgrade:
Use Windows Device Recovery Tool (download here:
http://go.microsoft.com/fwlink/p/?LinkId=522381 and FAQ here:
https://support.microsoft.com/en-us/...overy-tool-faq) to get back to 8.1 (if not already) - you'll need to connect your phone to the PC you installed WDRT
Go to this site: 14219-10586 htc w8 tmous (0P6B140) - Pastebin.com and grab all of the .cab file urls. These urls are from this thread: [W10M BUILDS] Update links collection (cab-f?€? | Windows 10 Development and Hacking)
This is the part that sucks... Paste each url into a browser to download the file (you should end up with 47 files) - on a side note, if anyone doesn't want to do this, I could paste a link to a zipped folder with all of the files
Place all the files into a folder named "cabs" in your C: drive (ex: C:\cabs)
Download and install the Windows Driver Kit from
http://go.microsoft.com/fwlink/p/?LinkId=526733
Open command prompt (windows + R then "cmd") and enter this command (places you in the proper folder to execute the next command): cd C:\Program Files (x86)\Windows Kits\10\Tools\bin\i386
While your phone is connected to the PC, run the command: iutool.exe -V -p "C:\cabs" - it will take a while to execute as it transfers, then installs all 47 files. I think it took about 75-90 minutes for me.
Once that finishes, you'll be on build 10586.11
See this thread for the working hyperlinks etc:
http://forums.windowscentral.com/htc-one-m8-windows/426772-5.htm