Will my motherboard support my ram?

Hello ! So my motherboard has 4 slots and supports up to 8 gb of ram atm i have 4gb and i am thinking of adding 4 more but the Current ram i have occupied all of my slots so i am thinking of getting Ram2x4Gygabite so it will take only 2 of my slots and reach the limit . My question is do i have to fill all the sockets with Ram4x2Gygabite or will it run with Ram2x4Gygabite?