Your AC sits on a 14" x 14" hole. There are four long screws threaded from below that hold it on. The gasket between the AC and your roof is what makes it water tight. So, remove the ceiling package, remove the four long screws, remove the AC. You have a 120VAC connection, so turn off the circuit breaker first. If the thermostat is remote, there will be wiring for that also. AND if you have "duct work" for the AC (remote vents it blows through). You'll see where the roof has a cavity the air blows into. Use metal tape designed for heater ductwork to seal it the way it was when you took it apart. Clear as mud? I do this type of work frequently, it's not that hard with a little patience.