I have a brother in the tire and automotive/ag service business. Breaking the tire bead loose from the rim is the most difficult part of dismounting tractor tires. He has an air powered ram bead breaker on his service truck. Without that a heavy hammer and a blunt, flat bar combined with sweat and time. They can be stubborn if they've been there for years and the bead seats on the rim are rusty. Once the bead is freed from the rim seat the job is easier. Three tire tool/bars; start with one, then the second, then the third (all spaced a few inches apart). Then remove the middle and get another bite past either of the two end bars until you have worked your way around. Take the tube out (hope it isn't stuck to the rim). Then do the same for the other tire bead. Just be sure to take both sides of the tire off the same side of the rim - just kidding, that's obvious. Oh, generous application of tire lubricant is also indicated.