Only do this when the engine is cold.

Use a socket designed for spark plug removal, with a rubber insert to grip the plug, otherwise you'll loose the plug inside the fan housing. Never use plugs with the screw-on 'nut' at the top either, for the same reason. The nuts have a habit of falling off and can drop down into the plug hole when you remove the plug. Always begin with just your fingers on the socket, not a ratchet bar, when you're fitting the plugs back in. The cylinder head thread is aluminum and the plug threads are steel, it's easy to cross-thread them, strip them, or just wear out the threads if you force them. When you're sure the threads are engaged (try turning them counter-clockwise til you FEEL as slight klunk as the first male thread drops into the first female thread), tighten the plug as far as you can by hand, then fit a torque wrench, and tighten to about 3.0-3.5mkg. A tiny bit of high temperature anti-seize on the plug threads will prolong the life of your heads by making it easier to get the plugs out next time, without tearing out little chunkies of the (soft) aluminum heads due to galling of the steel against the aluminum. Too much anti-seize with short the plug, so go easy.