Doing the replacement is pretty easy as long as you have the right set of tools. You’ll need: a penny, a set of Torx screw drivers as well as a Phillips screw driver.
1. Turn the computer upside down and take out the battery with a penny if you have the old white MacBooks. If you’ve got the new Unibody MacBook (evident from the “rubbery base" that runs the entire face of the bottom) then you’ll need to break out your Torx screw driver and get busy. Make sure that you take note of which screws are being pulled out from which side. I personally prefer using an empty ice tray, but you could use anything that has compartments in it.
2. For the Unibody MacBooks, you remove the Bottom cover while for the old white MacBooks you’ll need to take the battery out and then unscrew the L-bracket which lines the edges of the battery bay. While gaining access to the internals of the Unibody computer may seem hard, it is actually a lot easier because of the fact that there are no screws on the side that need to be removed like it is with the old MacBooks.
3. For the Unibody MacBooks, lift the bottom cover out and then pull the grey and black cross that is connecting the antennas out. For those of you with old white MacBooks, you’ll need to pop out the keyboard/trackpad ribbon before you get a chance to see your MacBook’s innards.
4. Replace the Airport Card with a new one and plug in both the antenna cables.
5. Follow steps one to three in reverse to get your MacBook back to its pristine state!
If you're still having issues when it comes to figuring out how to replace Airport Card on MacBooks, then have a look at The Quick MacBook Airport Card Troubleshoot article and this article if your MacBook's Airport card keeps on disconnecting.