The best way is to try it. Because some motherboards may work that 8GB even though it "only supports 4GB", while some motherboards may not. It's sort of a hit-and-miss. The worst that can only happen is that the 8GB (2x4GB) ram you have will only work like a 4GB (2x2GB)... and make sure the 8GB actually fits into that motherboard slots (since you did not mention any brands/models of both the RAM and the Motherboard). So, my recommendation, just check it out, nothing dangerous will happen.