haynes manual is your best bet. Basic guide is:
- remove exhaust down pipe: separate from manifold, 4 studs, disconnect from rest of exhaust (usually an exhaust clamp). Sling it out of the way.
- disconnect offside driveshaft from gearbox
- start undoing all the 10mm bolts around the sump, there's something like 15-20 of them in total. Two are covered up by the gearbox, you can access them by removing the bottom cover from the end of the gearbox (a single 11mm bolt) and then turning the engine over by hand until you see two cut-outs in the flywheel appear, these will line up with the two bolts so you can fit a 1/4" drive 10mm socket on an extension bar in.
- once all bolts are out (double check you've got them all) the sump should come free with a couple of taps by hand.
- remove all traces of old gasket from both the sump face and the block face.
- in theory it's then just a case of putting the new gasket on and offering the sump back up and bolting it on. However, I always find they seal better if you put some silicon sealer between the gasket and the sump. I generally apply it to the sump, leave it 1/2 an hour so it just starts to go off, then put the gasket on and bolt everything back together. Then you want to leave it a good while for the sealer to cure before putting oil in and using the car, overnight is best if possible.