1. Hi. Start by turning off the phone. To do that, press and hold the Power button.
2. When the phone is turned off, press and hold Volume Down.
3. Still holding the button, connect the phone to the PC via a micro USB cable.
4. Let go of these buttons when a Fastboot mode menu shows on screen.
5. Superb, you are now in Fastboot mode. Navigate this mode using Volume Keys; select options with Power button.