1. Begin by switching off the device by holding down the Power key for a short while.
2. Next, press and hold the Volume Down + Power button for a few seconds.
3. Use Volume buttons to select Recovery. Confirm with Power button.
4. Wait for the phone image to appear and press'n'hold the Volume Up & Power buttons simultaneously.
5. Good job, you are in Recovery mode. Navigate it with Volume buttons; select options with Power button.