Knowledge that you need to know:
To unlock your bootloader goto htcdev.com
Left-shift click inside a folder and click “open a command window” to open a local cmd window and run commands from there.
Access bootloader by powering the phone off and then holding the power button and the down button.
Install a custom recovery by flashing it. Have the phone in fastboot and connected to the pc. You will need fastboot.exe in the same folder as the recovery image. Then enter in command window : fastboot flash recovery recoveryname.img
Phone : ***HTC Desire 816 Virgin Mobile***
Please use TWRP. I have not used CWM ever since I tried TWRP. Always make sure to use the latest version of TWRP. Which can be found here. ( I use openrecovery-twrp-126.96.36.199-a5.img )
1) Have TWRP installed as your custom recovery ; Boot Unlocked
Information at top on how to install custom recovery and boot unlock
2) You need the OTA Lollipop update for the HTC Desire 816 – 1.4 GB
3) Here is a folder containing everything else that you will need.
Make sure to keep all files together in the same folder.
4) Adb Drivers and HTC Drivers have to be up to date
Always backup your phone before doing anything that could possibly do damage to it. Whenever you do a backup always put a copy on your PC. Go to your custom recovery and use backup option.
Now you can -> wipe -> advanced wipe -> dalvik, cache, data, system
Flash and Lock.
Reboot to Bootloader *Do not install supersu*
Select fastboot and connect to your pc
Flash the StockRecovery.img file
Run oem lock.bat
Put your phone into bootloader -> fastboot -> connect to pc
Open the OTA Lollipop Update that you downloaded and wait.
After the update finishes that phone may lock onto white HTC screen. Simply shut phone off and turn it back on. Now just wait as your apps update and voila!