It's dead easy. Just lever them both out very carefully with a flathead screwdriver - be very careful not to break/bend any pins. Then just put them back in each other's sockets. Of course be sure to notice which way they go round... don't fit them wrong
If you need some pics of A500 CIAs they look like the top picture here:
http://www.amiga-hardware.com/showha...gi?HARDID=1455
Have a look... if you don't fancy doing it get a friend to help.