This post is about how to clean a Windows.old folder, when you upgrade Windows the installer create a folder Windows.old , but you can remove this folder. First you need to install a Desktop-Experience, by default this is not installed in Windows Server
>Install-WindowsFeature -name Desktop-Experience -IncludeManagementTools
Reboot the system
Open the Server Manager - Tools - Disk Cleanup
Select the Drive C:
Check de option "Previous Windows installation(s)"
Simple and you safe some GB in your server.