How Do I Pair An Apple Remote To My Mac?
Once you are logged in to your Mac, position the remote 2-4 inches away from the infrared sensor in the front of your Mac. Hold the "Menu" and "Next" buttons at the same time for about five seconds. A chain-link lock will appear in the middle of your screen once the remote is successfully paired.
You can unpair the remote by going to System Preferences > Security and click Unpair.