How to change the distributor on a 1994 2.0l gls Vauxhall Cavalier?

My car doesn't start and at first I thought it was due down to the weather being so cold and wet but after spraying WD40 around the engine, it still won't start so i'm now thinking it maybe the distributor that's at fault. I have a Vauxhall Cavalier GLS on an L plate (1994), it's a saloon with 5 gears on a manual gearbox, the engine size is a 1998cc.
When I try to start the engine, it does turnover but simply doesn't spark into life, hence why I was thinking it's the distributor. Therefore, does anyone know step by step instructions on how to change this should I purchase a new one? Also, where I could find a cheap new distributor (as opposed to a used one)? I'd really appreciate your help!
Thanks so much

Jenny
January 2010