What is Windows.old folder in Windows 10? Can I delete Windows.old then? Well, these are the questions that you might ask after installed free Microsoft Windows 10 Pro. Windows.old folder was created when you upgraded to Windows 10 from previous Windows 7 or 8.1. Some files used by your previous version of Windows will be left in the Windows.old folder. These files will be automatically removed after a month of upgrading or you can use Disk Cleanup to remove them yourself now. You won’t find this folder on clean Windows installation. In short, you can remove Windows.old folder safely. But lose the chance to revert back to previous version.