This window zip tool can be used as a last resort. Best first to push on the sides of the windows and push up or pull down to free the paint-over. Obviously, this doesn't always work so zip it! If you are painting wood windows leave them open at least an inch for a couple days and move them up and down a bit whenever you walk by. This should prevent painting them shut. Never pry wood windows away from the jam, they will be permanently dented.
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