What John&Joey said. I use Schaeffer's all trans supreme myself, but the method of disconnecting the return cooling line at the rear of the trans is by far the easiest and cleanest method out there if you're a DIY type. Takes about 18 quarts total (about 2 are wasted) but it completely replaces all the trans fluid and takes little time.
I use a clear hose to a bucket sitting by the driver's door so I can watch as the fluid stops running and turn the engine off. I also cycle the gear selector through all the ranges to get fluid through the whole tranny. I then then refresh the pan through the dipstick tube with the same quantity that came out. Use a bucket with quart markings so if 5 quarts come out then you put 5 quarts back in. You know you're good when the fluid coming out of the tube is nice and bright red.
Or just take it to a service shop. Good luck.
Vince