Release the locking mechanism on the top of the lower window sash in the frame. Remove the interior jamb bar that crosses the top of the lower window sash. Unscrew the bar from each side of the window, using a flat-head screwdriver, and pull it free.
Slip a putty knife into the window frame at the upper corners of the sash. Slide it between the side of the sash and the jamb liner, the vertical ridge inside the window frame that guides the movement of the sash. Begin at the point where the top of the sash meets the liner. Work the putty knife downward to release the latch that holds the window in the jamb liner. Raise the window in the frame about three inches.
Tilt the top of the window sash forward from the frame until the sash lies parallel to the ground. It will still be held within the frame with just the bottom of the sash remaining in place.
Lift the horizontal sash two inches in the frame to clear the retainer clips on the sides of the sash. Rotate the sash within the frame counterclockwise until the right bottom corner clears the frame. Pull the sash from the window
Remove the jamb fillers in the jamb liner, located in front of the upper sash.The fillers help hold the window vertically so it won't fall inward. Pry the fillers carefully from the window jamb with a flat-head screwdriver, then rotate them from the groove. Remove the lower jamb filler beneath the upper window sash using the same process, so that you can lower the sash within the frame.
Lower the upper sash within the window frame four inches. Press the sash-release latches on the top edges of the sash inward, unlocking the sash from the window frame.
Tilt the sash forward until it's horizontal. Lift it two inches within the frame to clear the retainer clips. Give the sash a counterclockwise turn to clear the frame and pull the upper sash free.