In order to hard reset a HTC Butterfly, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
HTC Butterfly device will be brought back to the default configuration of a brand new device.
1. Turn off the phone.
2. Press'n'hold the Volume Down + Power button.
3. Let go of these buttons when Bootloader mode starts.
4. Select the Factory Reset option.
5. Your phone will restart and reboot, congrats.