Soo download the Rom on your comp... I assume you have Fastboot/adb set up . Take the boot img out of the Rom zip and I'm just going to link you to a tutorial
---------- Post added at 06:38 AM ---------- Previous post was at 06:37 AM ----------
Flashing boot img through fastboot...
download the file in the link which above which will include adb and fastboot....put that on your computer somewhere you can find it.. now take the boot image out of the Rom zip and place it in that folder... Boot your phone into bootloader scroll down and select fastboot and now open a command prompt with in the fastbootbadb folder on your comp and type to command without the quotes "fastboot flash boot boot.img"...now go wipe in recovery and install the Rom it doesn't matter if you keep the boot img in the Rom zip or not
So do that here are you're steps
Fastboot flash boot.img
Proper full wipe
Flash Rom and enjoy