When you are installing a new operating system or upgrading your current operating system, you may want to delete the current operating system off your hard drive to start with a clean setup. Deleting an operating system off a hard drive will delete all data on the drive, so back up all important files before deleting the operating system.
Insert the Windows installation CD into your disk drive and restart your computer.
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Hit any key on your keyboard when asked if you want to boot to the CD.
Press "Enter" at the welcome screen and then hit the "F8" key to accept the Windows license agreement.
Press "esc" to view a list of all the operating systems currently installed on your hard drive.
Use the up and down arrow keys to highlight the operating system partition that you want to delete.
Press the "D" key on your keyboard and then press the "L" key to confirm your decision to delete the operating system. Depending on the amount of data on the hard drive, the deletion process could take up to 30 minutes to complete.