Since the installation of Windows 10 (from Windows 7) a few weeks ago, I've been having trouble trying to delete duplicate files, using CCleaner. Most of these files have 'old windows' in their text (probably relating to my now defunct Windows 7). I have never had so many duplicate files since the upgrade (maybe 300 or more). Every time I try to delete them, they just won't budge! I've uninstalled and re-installed CCleaner, and even carried out a system restore of my whole laptop, but they remain. Any help on this problem would be much appreciated. Thank you. Peter.
You need to properly clean the windows.old folder. Instead of using ccleaner to remove duplicates from it do the following
Open the windows.old folder
Look through it (paying special attention to the "program files" and "users" folders) for anything you might want to save and remove those to your new desktop.
Right click the system drive and choose properties. Go tools tab and click clean drive. Tell it to clean system files (will ask for uac approval). Roll down in the list to "old windows installation" (I believe it is called that) check it and run the clean.
Better instructions here (works for 7/8/10)
http://www.sevenforums.com/tutorials/19151-windows-old-folder-delete.html
Do note that after doing this you will no longer have the option to roll back to windows 7