if it's the same as in Germany you have to go to the official country's bank. No normal bank in Germany does change marks any more. Maybe ask in the hotel for the address(es). At least - Paris is the best chance of all to find a branch of the official bank at all. Usually only the big cities have one.

Baerbel near Stuttgart (where I can luckily find such a bank)

Mod´s note : Baerbel is right. You must go to the Banque de France, and there you will be able to change your FF. Ask your hotel to send you the nearest address and the opening times. Rgds, Covadonga