The phone follows the custom way of hard resetting an Android phone. It means that you need to power down the phone and pull the battery out for a few seconds then reinsert it back and press Volume Up + Power button for about 10-15 seconds until the Android logo appears. Select Wipe Data/Factory reset and wait for the process to complete. Reboot, then the phone will be restored to its factory defaults. The content you have saved on the internal storage and SD card will remain in its place. Only settings and installed applications will be removed.