Now to unlock your bootloader, which is required only when flashing a stock firmware image (not sideloading and update, which we'll get to soon), you must enter the below commands. Remember that when unlocking your Nexus' bootloader it will factory reset your device, so you will lose everything stored on it. If you have not yet backed up anything important on your device you can hit the power button while Start is highlighted in the Bootloader menu and this will boot you back into your device like normal. Now back to unlocking your bootloader.