Disk Cleanup option on drive’s general properties and cleanmgr.exe is not present in Windows Server 2008 or Windows Server 2008 R2 by default.

To enable Disk Cleanup, please follow the below steps:

1. Open “Server Manager”.
2. Click “Add Features”.
3. Disk Cleanup tool is bundled with “Desktop Experience”. Hence, place a check on it.
4. You will need to click on “Add Required Features” on prompt to proceed.
5. You will then need to click on “Install” button available.

Once the feature have been installed, the server will require a reboot to reflect the changes.