Whether you've recently upgraded to Windows 10, or updated from Windows 8 to Windows 8.1, you may be running low on disk space. That's because Windows installs a completely new version and keeps the old one around just in case you want to go back (downgrade) to the previous version. Here we explain how to delete the Windows.OLD folder, and get back a huge chunk of hard drive space.
You should see Windows.old in File Explorer because it's not a hidden folder. Open File Explorer by pressing Windows+E and go to 'This PC' and then click on OS C: (it's usually C but may be another letter). After the 'Windows' folder should be Windows.old.
It contains files from your previous installation of Windows, which were either not required or can't be used with the new version. You don't need to keep these unless something has gone wrong with the upgrade and you need to roll back to your previous version. To see how much space this folder is occupying, right-click on it and choose Properties. In our case, it was using up almost 25GB - a significant amount if you have only a 120GB SSD.
But unless your low disk space situation is causing problems, we suggest leaving the Windows.old folder where it is until you've made sure you're happy with your upgrade, and all your files and settings are in place. Don't try and delete the folder in File Explorer, though.
How to delete Windows.old
Windows 8.1 and 10 will remove these files automatically after around a month, but you can get rid of them by running Disk Clean-up. To do so, go to the Start menu (or screen in Windows 8) and type Disk Clean-up. Run it and select your system drive (if you have more than one) as the drive you want to clean up. It will appear with a small Windows logo as part of the icon.
Click the button marked Clean up system files (it may ask you to select your system drive again - select the letter for the drive where Windows is installed) and the utility will then give you a list of items you can clean up. Tick the box next to Previous Windows installation(s) to make sure the Windows.OLD folder is completely removed. You may find other files in here you wish to delete to help with your disk space problem, so you can select those, too.
Now click on OK and select Delete files. Your disk space issue should be resolved.