To do the job right, you need about a case of fluid and a filter kit. Drop the pan, change the filter, clean the magnet and put that back together.
Through the inspection cover look for the drain plug. If you find a drain plug, pull it and empty the convertor. Refill the transmission. If there isn't a drain plug, follow the next step...
If there isn't a drain plug, you need to do a running engine flush. Disconnect one of the lines going to the transmission cooler (really doesn't matter which one) and route this open lines into a big drain bucket. top off the transmission fluid somewhat (don't even bother with the dipstick). Start the engine and keep adding fluid to the transmission at the same rate is is being pumped out the cooler lines into the big drain bucket. After several quarts, the fluid will start coming out clean. Stop the engine, reconnect the cooler line, adjust the transmission fluid level and you are done
When you think you have the fluid right, take it for a short drive (in and out of the driveway is fine). check it again. Then go around the block a time or two and make sure you shift into each gear a couple of times and check it again.
You have now just done a complete transmission flush and service job.