If you have Windows Vista and you want to upgrade to another versionfor example, from Windows Vista Home Basic to Windows Vista Home Premium, or from Windows Vista Home Premium to Windows Vista Ultimateyou don't have to buy a new disc. Each copy of Windows Vista actually has all the available versions on it, and you can unlock any version by paying for it online.
If you're not sure what version of Windows Vista you have, select Control Panel System and Maintenance, and click Welcome Center. Your version will be displayed at the top of the page. To upgrade to another version of Windows Vista, select Control Panel System and Maintenance System, and click Upgrade Windows Vista. Then follow the instructions and pay online. You'll be instructed to insert your Windows Vista disk into your PC, and you can upgrade directly from that disc. You can, of course, also buy an upgrade disc if you would prefer not to pay online.