When you install Windows Vista Service Pack 1 on your computer, the SP1 installer will not remove the older versions of Vista files from the hard drive. These older are required if you decide to uninstall SP1. If you are satisfied with the performance of Windows Vista SP1 and don’t plan on removing it, you can safely delete these files. This process is as easy:
Open your Start Menu and in the “Start Search” field, type “vsp1cln.exe” then press enter. You will be asked if you really want to continue, to which you should press “y”.