Disk Cleanup is one of several features which are not installed by default on Windows Server 2008. To use the Disk Cleanup (cleanmgr.exe) on Windows Server 2008, you will have to install the “Desktop Experience” feature on the machine. To install Desktop Experience follow the below steps simply open the Server Manager and select Add feature, then select Desktop Experience.
After Desktop Experience has been installed, you can find the Disk Cleanup tool under the System tool subcategory :
Start > Programs > Accessories > System Tools > Disk Cleanup