As you can see from the above post, this is no quick and easy oil change. There is no drain plug to open, it's just not that simple. The above post misses one important thing, dropping the pan to be able to change the filter. You don't 'have to' change the filter but why do something half way? and... getting a good look at the contents of the pan gives you great insight into the health of the tranny.
My suggestion: take it to a tranny shop and let them do it. They'll flush the system and change the filter too.