A simple way to delete an undeletable file

I prefer alternative 3 but this option may save time if multiple files are to be deleted.

Disk Cleanup will remove all files stored in a folder named Windows.old in the drive's root if the option Remove Previous Versions of Windows is selected.

1. Create a directory named Windows.old in the drive root.
2. Drag and drop undeletable files and folders into that directory.
3. Run Disk Cleanup selecting the option Clean up system files\ Files to delete\ Previous Windows installation(s).