Doing this is easy.
There is a drain plug on the very bottom of the tranny.
Removing this plug will allow the fluid to escape.
You will drop about 4 qts of oil this way.
Replace the drain plug and then pour in 4 qts of fresh ATX oil.
Use MERCON ATF Fluid.
AMSOIL is the best brand you can buy, and Mobil 1 runs a close second.
Do not use anytyhing that is labeled as Mercon V.
Our transmissions were not built for use with Mercon V.
After you fill the tranny, start the engine and move the shifter to 1.
Then back it thgough all the gear positions till you get to P.
Check the fluid level and make sure it is full.
Drive the car for a day or so and then do it all over again.
After the 3rd time, you should have changed at least 75% of the fluid.
You won't get 100% of the fluid unless you take it to someplace that does a flush,
not a POWERFLUSH,
or you drop the tranny and disassemble it.
Flushing and POWERFLUSH are not the same.
Don't let anyone tell you anytyhing different.
Powerflushes use additives to remove built up varnish and settlement.
A Flush only uses NEW ATX Oil.
The only problem you may have is finding a local shop or Oil Change center to take your waste oil off your hands.
They may charge you a small fee to dispose of this waste oil.