Classic architecture generally made the width of the Frame of the window on the second story the width of the Glass of the window on the first story, a subtle, tapering effect.

I would probably consider the Surround of the window as a part of the equation in determining the upper window width. So, I would probably make the actual window narrower on the second, although maybe not by some precise width. You don't want the upper window to appear top heavy compared to the door.