On your smartphone go to Settings> About> and click 7 times on build number
Still on your smartphone go to Settings > Developer Options
Enable the following options: OEM Unlock and USB Debugging
With the unit off press the following buttons at the same time: Power + Volume Minus the unit will enter fastboot mode
Now on your computer, open the Minimal ADB and Fastboot program
In ADB type fastboot devices and press enter: soon after the connected device will appear
Type fastboot oem unlock and hit enter
On the device you will confirm the unlock, use the volume keys to get to the UNLOCK THE BOOTLOADER option and press the power button to confirm your choice
Your device will restart and the bootloader is unlocked