Hard Reset HTC Sensation XL

First method:

1. Turn off the device by using Power button.
2. Press and hold Volume Down + Power button at the same moment.
3. Release when u see three Android images.
4. Navigate to "FACTORY RESET" by using Volume buttons, and to choose option use Power button. 
5. After this your HTC device will reboot itself.

Second method:

1. Start by going to Menu thenSettings and then Backup & reset.
2. Find Reset phone and select it.
3. Select Erase all data if u want delete all media from your HTC device.
4. Tap OK.

WARNING !
Hard Reset will erase all of your data
All described operations you are doing at your own risk.