You basically need to take a hacksaw to your existing system (assuming you have the OEM "cannon") as it's one piece. Not a difficult job if you have a little hand to eye coordination though
Choose a can you like the look of, if you are running it with the baffles in they all sound very similar anyway. Delkevic and Fuel cans often get mentioned as they are relatively cheap and well made. Make sure it is stamped with the BS/E mark to ensure it's road legal.