Most all riding mowers allow you to lower the blade assy to it's lowest position, then unpin it from the tractor. They're heavy so be careful. Usually the only belt you need to unhook, at this point, is from the motor pulley. Once unpinned, just slide it out from under the mower, and MOST of the ones I've seen, have a diagram printed on them, showing the belt layout.
Once removed, you can do what ever you need, and slide it back in and hook it back up. Just pay attention to where the pins come out. If necessary, take pics with a digital camera. Excellent reference.