Allen key to undo the cover bolts, think it might be 5mm.
10mm hex socket and extension to undo the coilpacks and lead clips.
Spark plug socket (I always forget the size as it's the smaller one in my set) and longish extension with wrench.
A half decent socket set should include everything you need.
Tip: You'll see two ventilation hose that cross over the top of the plugs/leads, the rubber will have hardened if they haven't been replaced for a while. Heating them up with a hot hairdryer will make them more plyable and much easier to remove, a good opportunity to replace them but this isn't always essential.
Only do one spark plug at a time so you don't get the leads mixed up. When you're screwing in a new plug initially just use your hand with the extension and socket and not the wrench, this should ensure that you don't forcibly cross thread the plug. When you do tighten it with the wrench don't over tighten.