getting rid of old vista windows folder after installing 7

I recently updated to windows 7 pro from vista home premium. My laptop has two hard drives, C (w/ 30 gb and D (w/ 180 gb). Vista came on my C drive but I installed 7 on my D drive because it had more space. Now though my C drive still contains the Windows folder from Vista and it's taking up 20 gbs while the new Windows folder for 7 is only using 7 gb on D. I already deleted the windows.old file that came from the 7 installation but whenever I try to delete the Vista Windows folder on C I get a message saying I need permission from trustedinstaller.
How can I get rid of the vista files because they are taking up way too much space?

Two ways to uninstall:

If you don't need any files on your old vista's partition, you can remove Windows Vista by reformatting the partition where it is installed.

1. Uninstall Windows Vista on a multiboot system

  • Insert the Windows Vista installation disc.
  • Click the Start button
    , click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator.
    If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
  • Type [DVD drive letter]:\boot\bootsect.exe /nt52 ALL /force and then press ENTER.
    For example, if the DVD drive letter is F, type f:\boot\ bootsect.exe /nt52 ALL /force.
  • Eject the Windows Vista installation disc.
  • Restart your computer.
    Your computer will start in the previous version of Windows that you have installed.
  • Delete Windows Vista files and folders, such as the Program Files, Users, and Windows folders, manually.

  • You can also remove Windows Vista by reformatting the partition where it is installed, but do this only if that partition is not the boot partition. Reformatting the boot partition might make your computer unable to start.

2. How To Uninstall Windows Vista Using EasyBCD | Windows Vista for Beginners

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