Anyone have any good ideas how to cool both upstairs and downstairs?

this is the first time I've lived in a two level home. its a two story townhome. I have all my vents downstairs shut except for one in the living room and I have the upstairs vents wide open. I still can't figure out how to keep both levels at the same temp or close to. I have a little boy with severe eczema that is aggregated by too cold or too warm temperatures. does anyone have any good ways to efficiently keep temperature equilibrium on both floors? thank you.