You need Odin installed on your computer. With your phone turned off, hold the volume down button and plug it in to your USB. This will put you in download mode where you should see a big yellow triangle on the screen. Then launch Odin, click the PDA button (VERY IMPORTANT), navigate to the kernel file, then click start. By default Odin should have the box checked for auto reboot but just make sure as when it completes the phone will, well, reboot.
Im guessing you'll need this too:
Odin
Im guessing you'll need this too:
Odin