Replace the plugs with the exact plug recommended by the factory. It will be listed in the owners amnual, usually on the inside back cover, but maybe in the engine data page.

The boots can be removed with a peg board hook. Find a hook with the pins that fit into the peg board spaced close to 17mm - adjust a little if necessary. Use a short piece of 1/4" pipe over the hook end (use a straight hook - like you would hang a hat on). Slip the fork over the metal boot and lever against the valve cover. One of the moderators, Gilly, recommends one of the old valve adjusting crowfoot tools, but I gave mine away some years ago (dumb!).