To sum it up in a few steps (do a search to see exactly what is involved).
1) unscrew FILL plug
2) unscrew DRAIN plug and collect the old fluid (try to use a graduated receptacle (pan/bucket/whatever) too see how much comes out. Over the years, people have reported about 3.5 quarts.
3) Screw the DRAIN plug in
4) Pump in the amount that drained out 3.5 quarts if not a little more.
5) Turn engine on and (easiest way) get a scan/OBDII reader to see when the transmission gets to about 100-115 degrees. When it does.......
6) Unscrew the "check plug", some fluid may come out, when it becomes a "trickle", then screw it back on. This indicates that the fluid level is correct.
7) Screw DRAIN plug back on.
8) Have a beverage of your choice.
9) If you want ALL (in theory) of the fluid out using this method, do this again a few times after driving it a couple of days in between drain/fills. Eventually, you will drain out most of the old fluid. This is how I've done so in my 2007 Honda Civic. It currently has 386K miles on it. Original tranny and shifts like new.
I'm gathering up all the necessary hardware to do this in the near future. Sorry if this is overly simplified, but it is basically what you do to do it the right way. If I missed anything, chime in!!