Instructions Unlock Bootloader HTC Desire 826
See for Guide here
Unzip adb file and copy twrp recovery.img in to adb folder.
Turned off Phone, then press the Volume Down and Power to enter the bootloader.
use the Volume UP-DOWN to select and press the power button to FASTBOOT
plug your phone into the computer
Right click on adb folder and press start command window here.
Copy past the command into window and press inter.
fastboot flash recovery recovery.img
if you twrp recovery img is other name plz rename it to recovery.img
It will run for about 1-2 seconds to complete. ok now the phone off by pressing the Power button for 10 seconds and then go back to the Boot Loader by pressing the Volume Down button and Power you will find the 2nd line after the word Fastboot is: Recovery. So you’ve done
Copy the downloaded root file in directory of the memory card.
put the phone into Hboot (Shutdown completely .Press and hold the Volume Down button simultaneously press the Power button Hold the Volume Down button until it to be Hboot then let go)
Once start Hboot volum key used to move down the line Recovery. Press the power button to agree.
Select install zip from sdcard, press the Power
Select choose zip from sdcard, press the Power
Select the file (* .zip) that you just copied to a memory card, press the Power
Wait for it to run UP finished, restart your computer is OK