Effective ways to open locked windows include removing the glass, popping the spring bolt with a credit card, breaking the glass and forcing stuck lock valves until they release the window. The best method for a particular situation depends on the type of lock involved, its location in the building and whether the lock mechanism is indoors or outside.
Most windows in homes, apartments and offices have one or two locks. Each lock is connected to a screw or valve that opens and closes it. If the valves rust or get stuck in the closed position due to sloppy painting, the window cannot move. Rusty valves benefit from a liberal application of a hardware lubricant.
To open a window that is painted shut, cover the lock with a soft towel and gently knock it with a hammer. Tap the hammer from right to left. These and other screw locks open when turned counter-clockwise, and aiming the hammer blows accordingly encourages the lock to pop open.
Window locks are easy to reach from inside. It is much more difficult to open a window while standing outside. If the window is part of a door, it does not have a separate lock. Bypassing the window is still useful, however, because it makes it easy to reach inside and turn the doorknob. Insert the tip of a Philips head screwdriver into the bottom edge of the window and wiggle it around until it fits beneath the glass. Apply gentle, steady upward pressure until the window pops out.