Here posted in Novox Sticky Thread
To unlock your bootloader via HTC's official method, visit their bootloader unlock page:
HTCdev - Unlock Bootloader
Note that this method only works if you have the official software version 2.08.651.2 or higher (or HBOOT v1.5 or higher). This version permanently watermarks your phone, indicating that it has been unlocked. While you can manually relock the phone, the watermark remains. But in terms of enabling typical rooting functionality, such as installing a custom recovery and flashing custom ROMs, this method will allow you to do so. Once the unlock process is complete, take a look at this thread for specific instructions on how to get a custom recovery and flash ROMs:
[GUIDE] HTC Unlock Hboot 1.50 + TWRP Recovery 1.0.3 + Root + Flash Anything!