You cannot entirely drain the atx fluid (9 quarts) so this is really a dilute old-with-new process.
Here's an edited version of procedure from service manual:
Transmission Fluid Drain and Refill
Raise and support the vehicle.
Place a suitable container under the transaxle drain plug.
Note:
If an integral problem is suspected, drain the fluid through a paper filter. A small amount of metal or friction particles may be found from normal wear. However, if excessive metal and friction particles are present, internal service will be required.
Remove the transaxle drain plug and drain transmission fluid.
Add 4 quarts of Motorcraft MERCON® Multi - purpose automatic transmission fluid or equivalent meeting MERCON ® specification.
Start the engine and run through all gears for a total of five minutes at idle. Turn off the engine. (As an alternate, some owners just drive for a few miles or a day or so before the next step).
Repeat above steps (i.e. another drain/refill with 4 quarts) to help flush fluid from the torque converter.
Drain plug rather conspicuous when you look under car, it's towards driver's side from the oil pan drain plug (I'm assuming v6).
As you can see, prior post incorrect; there is no pan, only drain plug.
Torque for drain plug: 19-21 Ft-lbs.
