How to Fix a Window Jam
If your window is stuck, it’s very simple to get it unstuck. What you want to do is take the edge of a putty knife or some similarly sharp, slender object and work it around the edge of the window, as much as you can to loosen up whatever might be catching. You may also even go across the top of the window in there and you may end up also needing to go from the inside, which may require you removing the screen or the storm window. But try this first - go all the way around with the putty knife to see if that helps any. Once you get it open any amount at all, you can really force it up, and then what you want to do to make it easier in the future is to sand around the inside edge to remove whatever is catching the window and rubbing and causing it to stick. And then for extra good measure, take a candle and rub around. This will put wax along the edge there which will further lubricate the window so that it operates smoothly.