Windows Update leaves lots of files, which you don’t need anymore. The Disk Cleanup utility lets you remove those files.
Unfortunately the tool needs to be “installed” on Windows Server 2008 and 2008 R2. There is a Guide over here –> http://technet.microsoft.com/en-us/library/ff630161%28WS.10%29.aspx
Instructions for Windows Server 2012 are within the comments of the linked article.