Yes your local Dealer can do the OS upgrade - assuming you need it? If you can get the version number you have installed already then someone on here will be able to work back to what version of the OS you have installed. Discs are approx £12-50 from a Dealer, and it takes about 5 mins to update to the latest version (V32 if memory serves) released for the Mk4 DVD based nav.
This
Guide on Xoutpost will help you too.....
Richard