What operating system are you running?
Normally I would say to open up Windows Explorer and right-click the Windows.old folder, then left-click on Properties. Then go to the Security tab and give your userid full permissions for the folder, either through the Edit button or the Advanced button. If there is a box to apply the changes to all subfolders and files, make sure to put a checkmark in that box (I think that's only present if you go through Advanced).