Deleting the Windows.old directory
Upgrading Windows may lead to a “Windows.old” directory. This is a safety measure, in case you need to downgrade to your old version. If after a while you realize that everything works fine and you are satisfied with the installation and upgrade of Windows, you may like to delete this Windows.old directory to save space — but Windows won’t let you!
Trying to delete the folder as administrator, or by opening an administrator command prompt, is useless. The only way to do it, is to boot from the Windows Repair disk and open a command prompt from the temporary Windows system this disk creates.
To make a Repair disk, go to Control Panel > Windows 7 File Recovery.