If you installed SP2 yourself, you can uninstall it. However, if your computer came with SP2 already installed (an integrated installation), it can't be uninstalled.
To uninstall SP2
1.Click the Start button , click Control Panel, and then click Programs.
2.Under Programs and Features, click View installed updates.
3.On the Uninstall an update page, click Service Pack for Microsoft Windows (KB948465), and then click Uninstall.
4.Follow the instructions on your screen.
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To manually install SP2 using the standalone installation package
1.Depending on whether you're running the 32-bit or the 64-bit version of Windows Vista, download the update for 32-bit versions or download the update for 64-bit versions.
•To determine whether you have the 32-bit or the 64-bit version of Windows Vista, click the Start button , right-click Computer, and then click Properties.
2.To install SP2 immediately, click Open or Run, and then follow the instructions on your screen. To install SP2 later, click Save to copy the installation file to your computer. When you're ready to install the service pack, open the file you copied to your computer.
3.On the Welcome to Windows Vista Service Pack 2 page, click Next.
4.Follow the instructions on your screen. The computer might restart several times during the installation.
5.After installation is complete, log on to your computer at the Windows logon prompt. You'll receive a message indicating whether the update was successful.
6.If you disabled your antivirus software, enable it again.
Service Pack Links:
For 64-Bit
LinkFor 32-Bit
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Witcher updates:
Link(Hope this helps, hope CH dont mind the links just trying help out)