How do I change the rear rotors for a 2002 Izusu Trooper II LS?

There should be some threaded holes on the inner face of the hub on the rotor. First get some WD 40 or even better is PB Blaster and spray it, let it soak and wipe off the rust and repeat. Let it also soak into the area where the hub and rotor meet as this is the sticking point. Let it soak overnight if possible.
Match a bolt to the thread of the hole on the rotor and start to slowly tighten it. Look for the rotor too move. If it starts to take too much effort, leave the bolt with the stress on it and repeat the PB or WD soaking procedure and try to loosen it again. That is how most Techs would remove it unless you have a giant puller which most do not. I have never had to resort to that and it does take some time to get them off as I have been in your situation before.