You'll need to download the free program from one of the links under 'downloads' center top of page. I usually use one of the MajorGeeks links. Install and run the program and brows the system information it gives. Although an older program it's still good for system info.
Open Everest home and in the right pane you should see a motherboard icon-click on it and click on another motherboard icon. Should give the mobo's details and name. Here's an example image; click here