if its from the sump, then you will need to jack up car, place on axle stands, drain oil into container, and dicard of properly, undo seal bolts, remove old seal and after cleaning bottom of sump, look out for magnetic plate, refit new seal, fill with correct amount/type of auto transmisson fluid,put car back on its wheels, start car, and keeping the brakes on, go though gears to settle fluid.you can get seal & fluid from motor factors give them reg. number for correct one for your car.
leaks can also come from drive shafts, torgue convertor,just need to look around. Good Luck.
hope it helps, August 2010