Hard Reset HTC Butterfly

First method:

1. Switch off device by pressing Power button.
2. Press and hold Volume Down + Power buttons.
3. Release when u see three Android images.
4. Select option "FACTORY RESET" to browse by using Volume buttons, and to choose option Power button.  
5. After phone will automatically reboot.

Second method:

1. Go to Settings and then to the Backup & reset options.
2. Select Reset phone.
3. Mark Erase all data if u want delete all media from device.
4. Tap OK.

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