Ok, once you unlock, download TWRP for your device. Use the link withe the rom, here on this site,
https://androidfilehost.com/?a=show&w=files&flid=318170. Re-boot your device to fastboot and make sure to copy the TWRP.img file into your ADB folder on your PC. Make sure you have downloaded ADB tools and installed them on your PC first. Once this is all done, connect you phone, now in fastboot mode, via a USB cable to your PC. Now at the prompt in a Command window, navigate to your ADB folder and type <ADB DEVICES>. You should get a return showing your device is connected. If it shows that it is connected simply type <FASTBOOT BOOT TWRP.IMG> let it do its thing. do not be impatient amd unplug it. It will boot into TWRP. Once in TWRP, select the wipe tab in the upper right hand potion of your screen. Then select the format data tab. A blank line will appear. On that line type in <YES>. Once the drive has been formated, reboot into fastboot. Run the <fastboot boot TWRP.img> command again. Once TWRP boots up, you should be able to see you phone and its storage on your PC. Copy the rom's zip file onto your device's storage (sd card). then proceed to the INSTALL button in the upper left portion of your screen of your device and select the zip file and swipe to continue with flash. Once completed with flash, disconnect from your PC and allow the system to reboot. This will take upwards of 10 minutes the first time, so be patient!