If you have already unlocked your bootloader,
you have the fastboot files on your pc. Flash
the kernel zip file in recovery. On your pc,
open the kernel zip with 7zip, copy the
boot.img to your fastboot folder. Reboot your
phone into bootloader, select fastboot on
your phone and connect to your pc.
On your pc, open a command prompt window
and change directory to your fastboot folder.
Type in the following code: "fastboot flash
boot boot.img" , without the quotation marks.
Make sure you only have the one boot.img,
or rename it to whatever you like. I keep
several different ones for different roms and
have them named for the rom they match.
Just replace "boot.img" with whatever you