Delete the Windows.old Folder and Save Space (Again)
 

To keep on the safe side, Microsoft's install setup saves a full copy of your current Windows installation (that's the Windows.old directory right there), and while this will come handy in case something goes wrong or you need to revert back, it will also occupy several gigabytes of precious storage.

http://www.techspot.com/guides/1219-...ws-old-folder/