Free up Disk Space After Updating Windows 10 by Deleting Old Assemblies
The Windows 10 update retains files from your previous installation, so you can revert to it if you need to. Deleting these files can give you back up to 20GB of disk space.
If you have upgraded to Windows 10, you may notice that there is not enough disk space available. Windows preserves files for previous versions of Windows, so you can uninstall Windows 10 if necessary. These files can take up gigabytes of disk space. If you have a large drive, this may not matter much. But if you’re running low and happy with the Windows 10 installation, freeing up that space is easy. Just open the Disk Cleanup utility, click Clean Up System Files, and select the Previous Windows Installations that you want to uninstall and anything else you don’t. I managed to get back 22GB, which is a lot on my relatively small SSD.
How to Free Up Up to 20 GB of Hard Drive Space After Installing Windows 10 | WonderHowTo