Advisory: A master reset reverts the device settings back to their factory defaults. It will permanently erase all personal data, and content such as pictures, ringtones and apps that are saved to the device. Data stored on an SD card will not be erased unless otherwise selected. It is recommended that you save (backup) important data to your SIM, SD card, or a computer before proceeding.

Instructions:

1. From the home screen, press the Menu key, and then tap Settings.
   
2. Scroll to and tap Privacy.
   
3. Tap Factory data reset.
   
4. Tap Reset phone. Tap to check Erase SD card to remove all saved media and applications from an inserted Micro SD memory card.
   
5. If security is enabled, enter your unlock PIN, password, or pattern.
6. Tap Erase Everything.
   

Alternative Method

1. Press and hold the Power Key and the Volume Down key.
2. When the phone starts vibrating, release both keys.
3. Use the volume keys to scroll to Yes - Delete all user data and press the Menu key to select.
4. Use the volume keys to highlight Reboot system now and press the Menu key to select.