When you upgrade from Windows 7 or 8.1 to Windows 10, the software retains a copy of your old operating system just in case you want to revert. However, if you decide that you're happy running Windows 10 and don't want to roll back, you're left with at least 15GB of wasted space on your hard drive, all of it stored in a folder called Windows.old. If you simply try to delete the Windows.old directory in File Explorer, the - See full info at: http://www.gurusbest.net/2015/11/how-to-delete-windowsold-folder-in.html