Included with the Patch Tuesday updates last week was KB 2852386
, an optional update. This update changes the Disk Cleanup wizard to provide the ability to delete superseded Windows updates in Windows 7 SP1, reducing the space used by the WinSxS ("Windows Side by Side") folder.
Normally, superseded Windows updates can be removed with the installation of a Service Pack. However, since Windows 7 SP1 was released over two years ago, the size of the C:\Windows\Winsxs folder has grown significantly since SP1.
It is important to note that after running the Disk Cleanup wizard, you may not be able to roll back to a superseded update. In that situation, it will be necessary to manually install the superseded update.
Additional important notes and the TechNet article describing the change are available in my blog post, Improvement to Windows 7 SP1 Disk Cleanup