Hard Reset HTC One (M8) Eye

First method:

1. At the beginning turn off your phone.
2. Press and hold  Volume Down + Power at the same time for a few seconds.
3. Release held keys when you see Bootloader Mode.
4. Then press Volume Down to select option "Factory reset", and press Power button to confirm.
5. Well done!

Second method:

1. Push the Power button to turn on the device.
2. Then from Main Menu go to Settings and tap Backup & reset.
3. Next choose Reset phone and select Erase all data.
4. Tap OK to confirm your choice.
5. Success!

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