I have done this multiple times and the MB engineers deserve a hand of applause for designing in a torque converter drain. On most cars you have to pull the return cooling line from the radiator and drain out the fluid by briefly(!) running the engine, draining a qt or so at a time while replenishing the with the exact amount of new ATF. when the fluid looks like new ATF you are done. If you just bought the car it is probably OK to drop the pan and check for damage but I have never found enough to bother with. Leave the pan alone. I always add a magnefine transmission filter to the radiator return line which both filters and captures suspended magnetic particles:https://www.amazon.com/Magnefine-Magnetic-Inline-Transmission-Steering/dp/B0787KWZPS. NEVER EVER do a transmission flush. Many flushing systems can ruin the transmission.