You need to locate the current HF unit (HFW-1 box) which has all of the wiring connectors (antenna, speaker, holder, microphone) and replace it with the new 610 unit (TFE-4 box).
If the current HF set is already using the stereo speakers, then You don't have to rewire the audio and all You have to do is to remove the 6310 phone holder and replace it with the 610 input device (CUW-3) and external display (SU-11).
Thanks very much for your useful info.
I have some more questions, however:
-do you know where i should look for the HFW-1 box?
-Will the built in microphone work,
and- will the steering wheel buttons work for control of the phone?
The box is usually located inside the console, somewhere near the glove box would be a good guess. You can follow the wiring from phone holder, microphone or antenna - whichever seems easiest. Car service manual might be helpful when disassembling panels.
The microphone is the same on both kits (HFM-8), so there's no need to change it.
I cannot tell whether the steering wheel buttons are compatible with the new system or not. Probably such buttons are in some way connected to the phone holder connector of the box. As the 610 is using a separate input device (CUW-3) instead of such holder, the steering wheel buttons may become unusable.
Your local Mercedes dealer could have better information on the features of factory installed car kits, so it might be worth a phone call.