There are quite a few ways to remove them, depending on how stuck they are. The main thing to remember is to try and not bend the UTH too much or it may not work when you put it on the next tank. All the suggestions above are good ones for getting it off.

To stick it on the other tank, I suggest getting some aluminum tape at the hardware store and using that to stick it on the tank. I love the stuff and use it to hold the flexwatt down on my rack. I've also used it in my incubator to hold the flexwatt to the walls and to hold an UTH on the bottom of a 20L tank.