Loosen the trackpad connector by pulling the locking bar toward the battery housing, using the tips of your fingers.
Slide the trackpad cable out of the loosened connector.
Note: When reassembling the case, the trackpad cable can get stuck below the slot to the motherboard. It's possible to nudge it out slowly by gently prodding it on either side with a small screwdriver. You don't need to use much force to do this. Eventually it will just pop back out and you can reconnect as per the instructions above. Also, note that the locking bar comes loose so if you see a little piece of plastic lying around when reassembling, that's what it is. :)