If you need to remove Windows Vista SP2 from your computer, follow these simple steps:
Open Control Panel -> Programs -> Uninstall a Program
Or you may type appwiz.cpl in the search box available on the Windows Start Menu.
Click Service Pack for Microsoft Windows (KB948465), and then click Uninstall.
Follow the instructions and this should completely uninstall Vista Service Pack 2 from your computer.
Do I have Windows Vista SP2?
Use the Control Panel applet “Programs and Features” and select “View installed updates” from the top left of the task pane, under Windows, look for KB948465.