If the transfluid is that bad, the best thing to do is to take it to a shop and get a trans flush. They will get all the old trans fluid out and flush the internals. It will probably cost you about $125.00 or so with synthetic trans fluid. Draining and refilling the trans several times won't do what you need to be done. That won't get out out all the nasty fluid and contaminants. Also you don't have to worry about getting rid of the waste oil.
By the time you drained and refilled the trans several times, it would pay to get the transflush. Nomatter how many times you drain and refill you won't get all the shit out. Your trans and torque converter hold about 7-8 quarts, you will be lucky to drain out 4 quarts at a time, even with draining the torque converter.
Get the transflush, you are better off. I get the trans on my Windstar done every year when I take it to state inspection. The automatic transmission is probably the most neglected part of every car.