I asked a mechanic the same question. There are 2 ways. 1) It's very dificult, but space is limited and hard to reach, especially removing the wires. A mechanic has special tools for that. 2) sounds the best, but I haven't tried it yet. Remove the air cowl grate (by the winshield wipers) and you should be able to reach the plugs (and valve cover gasket...mine needs replacing) from above.