Window sashes work by moving up and down on tracks. The windows lock by resting the sash into the windowsill, locking it into the frame. Sash lock windows come in single-hung and double-hung varieties, and are usually easy to open. However, when the temperature or humidity changes, sashes may become jammed and not open. Wood sashes are especially problematic, because wood expands and contracts, causing the window to become stuck in its tracks. Sashes also can become stuck because they were painted shut. If the window frame and sashes become warped because of house settling, you may need a new window.
Place your hands in the middle of the window where the top of the sash is located. This is usually made of wood.
Press upward with your palms on the sash to free the bottom of the window from the windowsill. Push upward enough to give room for a hand to be slipped between the windowsill and the freed sash.
Place both hands underneath the freed sash, and push up the window.
If you believe the window was painted shut, use a sharp utility knife to score the groove between the frame and sash. If the window still will not open, proceed to the next step.
Wedge the blade of a putty knife between the sash and the frame. Tap the end of the knife lightly with a hammer. Repeat around the window between the sash and frame. If the window still will not open, proceed to the next step.
Go to the outside of the window, and carefully wedge a pry bar under the sill along the corner of the window. Tap the end of the pry bar with a hammer. Lay a block of wood under the pry bar to prevent scratching the windowsill, and use leverage to lift the window. Repeat for the length of the sill.
Once the window is open, sand any rough areas of the track with fine-grit sandpaper. Rub paraffin or beeswax onto the tracks to help the window from sticking again.