RV Repair: Aquamajic 3 seat and cover, lame question, first travel

Question
I hate to bother you with such a lame question but I am a newby to RV's. I just purchased my first travel trailer( its used ), its a 34 ft 1990 Bel-air Supreme. She is a little old and in need of some minor repair but I got one hell of a deal. My question is about the toilet, its an Aquamajic 3. I need to replace the seat and cover. I already purchased the new seat, but I cant get the old one off. The instructions in the box are for an Aquamajic 4. I tried to remove the seat the way the instructions said but it wont budge. I am affraid to use too much force- I dont want to break anything. Do you know any tricks of the trade to get the old one off?  Thanks for your time.

Answer
I checked to see if we had any old owners manuals available that might help with the problem, but I don't have any that are that old. Without actually seeing the toilet in question, I really can't give you too much advice. I would try the Thetford website to see if they have a way to answer your question. www.thetford.com
Thanks, and sorry I couldn't be more helpful.
Dave