You have 4 RAM slots with a maximum of 8gb. The problem you are having is that each slot only supports up to 2gb modules. To max out the board you would have to get 4x2gb RAM modules. If the slots accepted 4gb modules, the max would be 16gb instead...which is not the case.
You will need to return the current kit and get the 4x2gb modules if you want the 8gb. I have found the system scanner on Crucial's website to be extremely handy to find out what configurations will work. It's free and quick:http://www.crucial.com/usa/en/?cm_mmc=bing-_-us-_-brand-_-null&ef_id=U3VcWAAABV4ADK7N:20140524181609:s