1. First, power up the phone by pressing the Power button.
2. Next, hold down the Power and Volume Down buttons for a moment.
3. Using Volume buttons to navigate & Power button to select, choose the Reboot to Bootloader option.
4. Now choose the Boot to Recovery Mode option in the same manner as above.
5. Get ready to press'n'hold the Power and Volume Up buttons. Do it when an exclamation mark appears on the screen.
6. When in Recovery mode, navigate using Volume buttons and select options with Power button.