There are 2 plugs at the gearbox, 1 underneath to drain it and 1 on the front as an inspection to check your levels. Take out both to drain it, put the bottom one back in and fill with the req amount stated in the manual, put the inspection nut back in. I cant remember off hand the amount needed, download the manual, it tells you in there and also shows you which nuts to loosen too.
Its a simple job really when you know how.