Update 9th of March 2019: The following post was written for Windows 8.1, but is still applicable for Windows 10.
If you have upgraded from Windows 8 to Windows 8.1 you might have noticed that there is a directory under the System Drive called Windows.old. This blog post explains how to delete Windows.old in Windows 8,8.1 and Windows 10.
This folder contains the contents from the previously installed Operating System, and can safely be removed if you haven’t placed anything in the Windows directory that you need to retrieve.
Here is how you remove it:
1. Open Windows Explorer
2. Right-click C: and select Properties
3. Select Disk Cleanup
4. In order for you to be able to remove the Windows.old folder, you need to select Clean up system files. Because this is an elevated task, you might receive a UAC prompt. Press Yes at the prompt.
5. Select Previous Windows installation(s)
6. Select Yes at the confirmation prompt.
About the author
Daniel Classon works as a Senior Consultant at Mansoft, focusing on Microsoft Configuration Manager, Windows 10 and Powershell