There isn't a drain plug on the pan, so it can get messy. What I did when I had an auto tranny was unbolted the front or rear of the pan and then let all the old fluid drain into a tub of some sort. Then drop the rest of the pan. You'll see where the filter plugs into. Replace it, bolt it back up and fill it up with some ATF+4 that you can get from the dealer. I forgot how much it takes to fill it up though...it's been so long. Someone should know, or you should be able to ring up an answer with the search.
