How to remove the windows.old is still an issue on some servers. Well it is easy to remove but you will need a reboot.
What you need to do is install the Desktop Experience Go to the server manager and add new feature
Find the Desktop Experience and add this you will need a reboot.
install-WindowsFeature -Name Desktop-Experience –IncludeAllSubFeature
Now that we installed the Desktop Experience there is a new option if you do properties on the C drive.
Press the Disk Cleanup and a quick scan will find all the info that we need to remove the previous Windows installation.
Now the Cleanup is running and after this I have 28.5 GB free space