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

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

Factory Reset via Settings:

1. Open “Settings”
2. Access “Backup & Reset”
3. If your device is protected by a lock screen, enter your PIN/password and tap “Continue”
4. When ready, tap “Reset phone”

Factory Reset via Android Recovery:

1. Turn the phone Off if needed
2. Press and hold “Power” and “Volume down” at the same time
3. In the Boot Mode Selection menu, release the buttons
4. Press “Volume down” repeatedly to navigate the menu until you highlight “Recovery”
5. Press “Volume Up” once to select the highlighted option
6. At the “No Command” screen press and release “Power” and “Volume Up” several times to gain access to Recovery
7. Once in Recovery, press “Volume down” to navigate the menu and highlight “Wipe data/factory reset”
8. Press “Power” to select the option
9. Then highlight “Userdata only” or “Userdata + personalized content”
10. Press “Power” to select the option
11. Once done, highlight “Reboot system now” and press “Power” one last time