I'll try to describe the process on the 300TD. Remove the fluid return line from the reservoir and slip a long rubber tube over the end of it. Put the other end of the rubber tube in the top of a gallon jug sitting on the ground adjacent to the drivers side front tire. Crank the car up and let it sit there idling. As the level drops add new fluid and when you have gone through 2 bottles shut the engine off, refasten/reattach everything and you have replaced the fluid.
Not sure of the differences on your model but it should be basically the same thing.

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Jim