I am not sure what exactly you are trying to do. But if you are trying to close the gap up you would select ether edge boarder and extrude it over to the other edge boarder to close the gap. You then could select the verts that lie on top of one another or close to each other and merge them together. It is also good practice to make sure you keep good edge flow.
assuming you want to keep the window it just doesn´t make any sense to combine those 2 edges. there is no way in combining them without destroying the window!
and also regarding your other thread: yes keeping your geometry as clean and as low as possible but also as high as necessary is a good idea!
there is two edges from up to down right?
just select their vertices, in the middle there should be two vertices and merge them.. it will be just one edge...
Edit: I meant here...