1. Switch on your device.
2. Go to Menu > Personal Option.
3. Select Backup & Reset > Factory Data Reset > Reset phone.
4. Accept previous option > touch once again option Reset phone.
5. Your device will reset to factory settings, and reboots.
1. Turn off your phone.
2. Press and hold together Volume Down + Power Button for 15 seconds.
3. Once Recovery menu appears on the screen, release the buttons.
4. Select "wipe data/factory reset" by using Volume buttons, and Power button to confirm.
5. Then choose "Yes -- delete all user data".
6. Confirm operation "reboot system now".