Aren't there extra RAM slots on the motherboard (requires cover remove
Extra RAM slots not normally made end-user available
mihaly_k , I believe there will be one empty ram slot and one on board chip(see ram installation guide link below). Check your computer spec.s for recommended Ram upgrade(max.)using your manual or a search with your exact model#. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.
It's often cheaper for manufacturers to only buy one type of RAM chip ie. 2 slot supporting, and simply only install one physical ram slot, so Windows might see "two available" however that is what the control chip is seeing not the physical available slots. My Lenovo T440 is the same way.