How to delete Windows.old folder in Windows 2012 R2

I have run into this issue several times and thought to write a post for it:

http://social.technet.microsoft.com/wiki/contents/articles/15221.enabling-disk-cleanup-utility-in-windows-server-2012.aspx

What you need to install is feature:

• Desktop Experience 

This can also be done with PowerShell 1.0: Add-WindowsFeature -Name Desktop-Experience

In PowerShell 2.0, you first have to import the appropriate module manually:

Import-Module ServerManager

Add-WindowsFeature -Name Desktop-Experience

Then you can search for Disk Cleanup, and cleanup system installation files by following these steps:

1. Open Disk Cleanup by clicking the Start button 
2. In the search box, type Disk Cleanup, and then, in the list of results, click Disk Cleanup. If you're prompted to choose a drive, click the drive you just installed Windows on, and then click OK.
3. In the Disk Cleanup dialog box, on the Disk Cleanup tab, click Clean up system files. If you're again prompted to choose a drive, click the drive you just installed Windows on, and then click OK.
4. Select the Previous Windows installation(s) check box, and any other check boxes for the files you want to delete, and then click OK.
5. In the message that appears, click Delete Files.