the 2001-2005 civics automatic transmission don't have pans to drop. PLus the filters are meant to be changed. You would have to drop the whole transmission and split the trans block to get at the filter.
The best thing to do that really the easiest is get honda ATF-Z fluid that is specific to the civic transmission. drain the fluid trough the drain blot which fits a 1/2" or 3/8" drive ratchet (I forget which). Replace the fluid and drive for a bit 50-100 miles. Try to cycles through all the gears multiple times. Repeat this another two times and you should have 98% fresh ATF fluid in the transmission.
If you're so inclined you can through one of those transmission flushed in the mix before doing the first drain. However being that there is only 40K on you car you shouldn't need it.