Return or retain?

Hello, I did a Volvo V70 III D5 `09, >150tkm last week. In the purchase contract, the friendly person took all the special equipment that was stated on his homepage down from the purchase contract, with the statement that it might be very expensive for him, if something is stated, which is not installed, and I would demand it. – until now everything is available to me. On Tuesday I found out that in this a performance increase was carried out by software from Heico. – I had to point out to the dealer ;-), in the appearance was nothing specified. However, I am now very unsure because of the software found by chance, since the vehicle was also maintained by him check booklet. This software is still active according to his statement… The friendly person offers me a deletion of the software… The vehicle has an automatic transmission, how very “couldn’t” (must not necessarily have been heated up by my old opinion)? I tend at the moment to give back the vehicle, even if a familiar, which meant for engine development… the engine does not have anything to do with the engine, but of course – I don’t have a bad opinion.