Kolector said it. They're readily interchangeable. Many folks buy the jeep with both. Other than the potential wiring for the rear window (which likely wasn't done if the jeep didn't come with a hard top), he should be able to easily remove the soft top and put on the hardtop presuming it's a factory top and it came with all the right parts. While the 2 door hard top isn't terribly heavy, it'd be best to do it with two people just for the sake of the awkwardness.