I just replaced a rear rim on my '39 RC. The tire was stuck tight to the original rim. I was able to break the bead loose by driving my pickup front tire onto the tire/rim. The weight of the pickup (an F-150) was enough to break the bead loose, but it still had to sit there for about 15 min. to get the job done. After that experience, I took both rims to a tire shop. They had a device that clamps to the edge of the rim and pushed the tire off. It took them about 5 minutes to do what it would've taken me hours of backbreaking work to accomplish. I know how I'm going to handle tractor rears from now on. Dismounting two tires and disposal fee for one tire cost me $12.50. That's dirt cheap!
Now for the other tip. When you get your old tires off and the rims cleaned and painted, to mount the rear tires to the rims, mount the rims back onto the tractor. A wise friend told me "gravity will be your friend". He was right! I was able to put the tire on with my foot for the first side and only used the tire spoons a very little bit for the second side. Gravity kept the tube far away from the spoons so there was no chance of a pinched tube. NO scratches on the new paint and it only took about 10 minutes. One of the best tips I've ever been given.