First method:

1. In order to turn the device off press Power button for a while.
2. After that, press and hold  Volume Up + Power button at the same time for a few seconds.
3. When the device powers on, release the Power but continue to hold the Volume Up key.
4. Release Volume Up when you see the Android Recovery System.
5. Press Volume Down to choose "wipe data/factory reset", and then push thePower button to confirm.
6. Select "Yes--delete all user data". Use Volume Down button to scroll and Power key to select.
7. To restart the phone, select "reboot system now".
8. Success! The hard reset has just been performed.

Second method:

1. Press the Power button, until your device is on.
2. Then from the Main Screen choose Settings.
3. After that select Backup&Reset and tap Factory data reset.
4. Choose Reset phone and select Erase everything to begin hard reset operation.
5. Well done!