Sounds like they are baked on man. Twist the wire, try to get it to spin on the plug, once that happens, should be able to get them off. Don't feel bad I had to fight the wires on my 94 360, broke two wires in the process and pulled the boots off with pliers.
If your gonna replace the wires, use any means possible to get them off, but be sure to put a bit of silicone on the new ones in order to avoid this in the future.
Mutt