Cassette change

Focus-rider Posts: 126
edited October 2012 in Workshop
I'm just about to replace my cassette. I've got a 105 at the minute running 12/28 and am changing to ultegra 12/25 with ultegra chain. Is there anything I need to know about changing them or is it a simple like for like swap. Is there any spacers involved that need to added or removed. At once again :D