For my other cars, this is the typical procedure I use:
1. If needed, replace trans filter. Put pan back on.
2. Disconnect the atf return line from radiator.
3. Connect the return line to a waste container, preferably with clear tubing.
4. Start car and idle to pump out old fluid...stop when fluid stops coming out. You'll probably get a few quarts out.
5. Fill trans with new fluid through fill hole with equal amount of fluid that was just pumped out.
6. Iterate between Steps 4 & 5 until clean fluid comes out of return line.
7. Button everything back up and trim fluid to proper level.
I've done this for a number of cars. Be forewarned that this usually leaves a big mess under the hood and on the floor.
I don't know if this would be a good procedure to use on some Mercedes models, since a regular drain and refill (including torque converter) would probably get 80-90% of the fluid with much less mess.
95 E320 Cabriolet, 131K