WARNING! When you factory reset your phone, all your personal data stored on the phone’s internal memory will be deleted, including media files and ringtones, apps, contacts, downloaded content etc. Additionally, all settings will be restored to factory values, however data located on the SIM and SD cards won’t be affected.

NOTE: You can check this thread for a guide on how to back up and restore data on the device.

Factory Reset via Setting:

1. Launch “Settings”
2. Go to “Backup & Reset”
3. If your phone is protected by a lock screen, enter your password/PIN and tap “continue” to proceed
4. Tap “Reset phone”

Factory Reset via Android Recovery:

1. Turn the phone Off if necessary
2. Press and hold “Power” and “Volume down” simultaneously
3. Once in the Boot Mode Selection menu, release the keys
4. Next, press “Volume down” repeatedly to navigate the menu and highlight “Recovery”
5. Press “Volume Up” to select the desired contact
6. When prompted with “No Command” press and release “Power” and “Volume Up” for several times until you gain access to Android Recovery
7. Once in the Recovery menu, press “Volume down” to navigate it and highlight “Wipe data/factory reset”
8. Press “Power” to select the option
9. Next highlight “Userdata only” or “Userdata + personalized content”
10. Press “Power” to select the option
11. Then, once the phone has been reset, highlight “Reboot system now” and press “Power” one last time to confirm