Hi Alan,
Just be firm but gentle with the rings, practice getting the old rings off without breaking them, gently push them apart using both your thumbs, not too wide just enough for the opposite side of the rings to come clear of the piston. If you break an old you are doing something wrong so try a different way. To get the rings into the bore it is not going to be easy but my method would be to cut a strip of sheet metal about 25mm wide and long enough to wrap around the piston and overlap a bit then with a worm drive clip tighten it up so it is snug and the rings are compressed but not over tight as the sheet metal strip has to be able to slide off the rings as you gently tap (use the hammer handle lengthwise) to gently tap the crank back into position and the rings inside the bore. Then you have to be able to undo the worm drive and get the sheet metal strip out. Just go slowly and you should be ok. If it feels like the rings don't want to enter the bore you will have to pull it out again and make sure the sheet metal strip is holding the rings in. It has to go together gently, don't force it, this is where you can break a ring
