After an upgrade or a reinstall that keeps your files, Windows can leave a folder called Windows.old that takes tens of gigabytes. You can remove it, but only after you understand what it is for and have checked it for anything personal.
Windows.old (usually C:\Windows.old) is a copy of your previous Windows installation. Windows keeps it so you can go back to the earlier version if the upgrade goes badly, and it can contain old system files, program files and user profile folders.
It appears after a feature upgrade or a reset or reinstall that keeps your files. Windows may also remove it automatically after a period of time.
Yes, once you are sure you do not want to go back to the previous Windows version and the PC runs well. Deleting it through Windows does not affect your current Windows, your installed programs or the files in your current user folders.
If you are still unsure about the upgrade, wait a few days first.
You can no longer roll back to the previous version of Windows from Settings. You also lose anything that only existed inside the old installation, which is why the next step matters.
Open C:\Windows.old\Users and look for your old user folder. If a reinstall or an upgrade did not carry something across (documents, desktop files, browser data), copy it out before you delete anything. Windows.old is not a backup, but sometimes it is the only copy of a few files.
Open Settings → System → Storage → Temporary files. Wait for the scan, tick Previous Windows installation(s) only, check the size shown and choose Remove files.
Search for Disk Cleanup (or run cleanmgr), choose the Windows drive, click Clean up system files, tick Previous Windows installation(s) and confirm. Read the other ticked categories before you click OK.
The folder is protected, and forcing deletion by taking ownership or changing permissions is unnecessary and can leave partial files behind. The Settings and Disk Cleanup methods are the supported way.
Rain Cleaner (Windows 10/11, 64-bit) lists what it found, with an explanation for each item, before it removes anything. The Free version has no ads; Pro has a free 14-day trial (no card). Everything above works with Windows alone.
Last updated: 2026-10-01
Yes, if you do not need to go back to the previous Windows version and you have copied out anything personal. Use Settings or Disk Cleanup.
It varies, often many gigabytes. Settings shows the size before you remove it.
Windows may remove it automatically after some time, but you can remove it yourself when you are sure.
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