nightspeed is right. You have to use the original AP that was used to tune the car by the previous owner to unmarry it. There may be some kind of open-source work around but I would post in the Tuning Forum to see what the gurus have to say.
Also, if you are going back to stock tune MAKE SURE you are all stock under the hood (turbo, downpipe, ect). Because if you run on a stock tune with extra performance goodies you will do bad things to your engine.