A:AnswerIf you look at page 21 in the manual you can initialize the Bluetooth settings this will erase all Bluetooth related settings and you can start from scratch.
If you don't have the physical manual anymore you can download/view it for free online.
A:AnswerAn important first question: IF there is a "dash kit" for the car, it replaces the unit where your current radio is installed and then the new radio must go in this new kit.
Ask Best Buy associate(s) who would do the install. They are very knowledgeable and will recommend the best kit AND radio(s) for your BMW. You can then decide about a radio model.