If there is a easy way I didn't find it. I removed mine two weeks ago started by cutting foam with a sawsall then digging it out with garden shovels and had to cut off the top of the tank. I drilled holes in the sides of the tank used a hoist and put pressure on the tank then carefully pried the tank away from the foan on the bottom. It took time but the tank did come out. This was on a 81 with a 65 gallon tank. The tank appeared to be glued to the foam and had two pieces of wood across the top was not attached in any other way.
Good luck :P