On CF2 & CF3 models, unscrew oil filler cap. Remove upper rocker cover using a ribe 6 key to undo the four securing fasteners.
Unfasten all concerning route clips down to and including the lambda sensor and air conditioning unit (if present).
Carefully pull the plugs with leads attached, off of the four spark plugs. On early cars these will be on the opposite cylinder while on late cars they are on the same one.
Undo the 5mm socket heads that secure the whole coil pack rail, noting the earth lead on the right hand side of later cars.
Carefully lift the coil packs off of the spark plugs.
Clean out around the spark plugs as it is not unusual for oil to be in the holes due to careless filling.
Remove spark plugs and replace.
If you need to do a compression test only remove the left hand spark plug from each cylinder.
Torque up the new spark plugs, large ones to 30Nm and smaller ones to 10Nm.
Replace coil packs making sure that the flying earth lead is attached on later plastic rocker cover cars.
Push on plug leads correctly.
Connect route clips, lambda sensor and conditioning unit (if present).
Refit top engine cover and oil filler cap.