|If your Vista Ultimate is retail version, not OEM, then start your PC and boot into Vista Home Premium. Then pop your Vista Ultimate DVD into the DVD-ROM tray and close the tray. If autorun of your DVD-ROM drive is not disabled, a couple of seconds later you will see a menu on the monitor.|
If Vista DVD does not start automatically, with Windows Explorer, look into the DVD and click Setup.exe to start installation. You will see the same menu on the monitor as above.
Choose Install Vista. Then you will be given some options: Upgrade or Advanced. I do not remember the exact options. If you do not see " Upgrade " as one of the options, just quit.