Power off your phone.
1. Press and hold the “Power/Lock key” and “T” key of the QWERTY keyboard at the same time until the “Android system recovery” menu shows up.
2. Use the “Volume key” to scroll down and select “wipe data/factory reset”
3. Press the “Home key” to proceed to the next confirmation step.
4. Use the “Volume key” again to scroll down and select “Yes — delete all user data”
5. Press the “Home key” to perform hard reset. All user data will be removed and the device will be restored to manufacture default.
6. Press the “Home key” to reboot system.
You can also refer to the YouTube video here.