I think there is a special tool that is made to remove plug wires, but failing that, you can try a pair of pliers on the end of the plug wires, with a couple folds of shop towel between the metal and the rubber plug terminal to protect it. Pull on it firmly, while turning and wiggling it a little bit to help break the connectors free.

When reinstalling, may want to try using a very thin layer of dielectric grease on the insulators of the distributor cap to keep the rubber from sticking too hard to the cap.