When you install Windows 7 SP1 or Windows Server 2008 R2 SP1, it backs up all the files that it replaces. This is done so, if, should you choose to uninstall Service Pack 1 at any point of time, these backed up files are readily available.
However after a couple of months, if you are comfortable with SP1 and if you are sure that you will not need to uninstall the Service Pack, then you may wish to consider removal of several 100 MB of such back up files and reclaim disk space.
To do so, open a command prompt with administrative privileges.
To remove the Service Pack backup files online, run the following command:
DISM /online /cleanup-Image /spsuperseded
To remove the Service Pack backup files from an offline image, run the following command:
DISM /image:<path_to_offline_image> /cleanup-Image /spsuperseded
The /spsuperseded option removes the backup files created during installation.
If you wish to simply hide the service pack from the list of installed updates without actually removing the files, use the /hidesp option.
Deployment Image Servicing & Management (DISM) is a new command line tool which was introduced in Windows 7 to manage a Windows image or prepare a Windows PE image.