At a guess, what you think is an upgrade disk is the "Windows Anytime Upgrade" DVD. This disk contains ALL versions of Vista, and if you check, you will find that you have a licence key for a specific version (possibly stuck to the underside of the lap top). What this means is that you have a disk for the version you have paid for, but if you wish to upgrade to a different version, you can simply by a key top unlock that particular version and install it on your machine, without having to obtain another disk. The licensed version will have already been installed.