Use a crowbar to pry the extension jam to reach the window pane, and remove the nails and shingles around it before removing a casement window. Before removing the window, use a hammer to shatter the glass, but tap it firmly. Pry the molding loose with a hammer and putty knife to prepare for removing the extension jam.
Wear protective gloves and glasses when removing casement windows, and keep the top nails in place while working to keep the window from falling out. The window pane is only secured with nails and shingles. Use a shingle hammer to remove the shingles by inserting a shingle thief underneath for careful removal. Apply gentle strokes with the hammer to prevent damage to the shingles. Once the shingles are removed, the window pane can be removed when the nails are gone.
If replacing the casement window with a new window pane, use the back sticker to paste along the window edge to keep out moisture. Another option is to use a water seal and gasket to prevent water seepage. Use a level to check the wall, and install the new window by nailing the top nails first. Use a measuring tape to see if the pane is even, and secure the window with the remaining nails. Place the shingles around the windows with galvanized nails, and add a new extension jam for the inside of the house.