1. Turn off the device. To do that, press'n'hold the Power button for a few seconds.
2. Now press and hold Volume Up + Power button for a moment.
3. Release them when the Android Image appears on screen.
4. Open the Recovery Mode by pressing the Power key
5. Good work. Unless you messed something up, you should now be in Recovery mode.
6. Navigate it with Volume buttons. Select options by using the Power key.