Hard Reset HTC Flyer

First method:

1. At the beginning switch your device off.
2. Press and hold the Volume Down button, and then briefly press the Power button.
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. If the display is off, press the Power to turn it back on.
2. Afterwards go to Settings and then to Storage.
3. Tap Reset Device. 
4. Choose Erase Everything if you are sure you want to clear all your data. 
5. Select OK to confirm the whole operation.
6. Well done!

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