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