Buy or download the ZX-Haynes manual to do this job.
The complete procedure is described in this manual.
This book is a must have for the do it yourself mechanic.

Best thing is to buy the manual, cost about ? 27, always handy
to keep it in your car. You never know when you might need it.

If you want to download it and you can't find it by yourself, send
me an email and I can provide you a link.

Good luck