1. First, please turn the phone off.
2. Next, press and hold together Volume Down + Power button until the phone vibrates once.
3. Now, quickly release Volume down and press Volume up and you will see a new menu on screen.
4. Please, use Volume buttons and select the "Recovery" option.
5. Next, choose "Wipe the data/factory reset" option using Volume buttons to browse options, and Menu button to confirm operation.
6. Now, confirm operation: "yes - delete all data" with Menu key.
7. Complete the operation by choosing "reboot system now".