You already have GFI LanGuard installation without the Central Management Server (CMS) and want to know if it is possible to install CMS on the same server.
Central Management Server can be installed on a machine that already has LanGuard main application. Both programs come bundled with the same installer, and you will need to use the same installer used to install LanGuard for this.
Disable antivirus, unblock the LanGuard installer, run it, and leave the tick box checked for both the Central Management Server and LanGuard. The installer will detect that LanGuard is already installed and proceed with installing the Central Management Server.
More detailed information can be found in the Installing the Central Management Server article.