If you choose to install Windows 10 on the same drive where an existing installation is already present, the setup program will create a folder named Windows.old in the root of the drive. This folder will contain a full backup of a previous installation of Windows 8 or Windows 7, including the boot manager and installed apps. This is very handy if you plan to uninstall the currently installed Windows version and return to the previously installed release. It can also be useful if you forgot to transfer some files or settings to the new installation. However, if you are already finished with the migration, then Windows.old just wastes your disk space for no reason. Windows 10 got the ability to delete the Windows.old folder automatically in a recent build. Here is how to enable this feature.
Tip: If you are running an older build of Windows 10 or a previous Windows version like Windows 8, Windows 8.1 or Windows 7, you should use another method, explained in the following article:
To automatically delete the Windows.old folder in Windows 10, do the following.
- Open Settings.
- Go to System -> Storage.
- There, you will find the option named "Storage Sense". Enable it.
- Now, click the link Change how we free up space.
- The Change how we free up space page will appear. Under Free up space now, enable (check) the option Delete previous versions of Windows. See the following screenshot.
- To remove the Windows.old folder instantly, click the button Clean now. This will remove the Windows.old folder immediately.
You can of course also delete your C:\Windows.old folder using File Explorer or an alternative file manager, but the Settings application will resolve NTFS access rights automatically and delete all files which are not accessible from your user account. In case of manual deletion, you will have to resolve those access rights by yourself, otherwise you will not be able to delete the C:\Windows.old folder.