I never upgraded the Nav on my 2005 X5 4.4. I read some of the Nav forums but I'm not sure how to work it for my particular year/car/situation. I never messed with upgrading the OS or the actual DVD disc. All parts/software are original to the 2005 year. What is the process for upgrading to the latest navigation? Do I need to upgrade the OS and the disc? If I just upgrade the OS, will my current DVD Nav disc still work? What should I do? Thanks in advance...