1. Switch off the phone by holding the Power button.
2. Then press and hold Power button + Volume Down button for a while
3. Menu with two options should appear before you. Let go of held keys.
4. You need to select Enter recovery mode. To do that, use Volume buttons to scroll and Power button to select.
5. Done, you're in the Recovery Mode.
6. Use Volume buttons to scroll and Power button to select options.