I have just completed this job on my "53"plate Zafira. You will need to remove the oil filler cap, remove the plastic "eco" plate under which you will find the "Coil Pack". Disconnect the wiring loom on the right hand side and remove the four retaining bolts in the top, carefully lift off the "Coil Pack" and put it somewhere safe, this will cost you over £100.00 to replace. Below it are the four plugs, these are set quite far down and I strongly recommend that you use a good plug socket and wrench to remove them.
Put back together in reverse order and your car should run sweet.