To replace the window on a door, use a putty knife, and remove the caulking and paint around the pane. Take the window out, using a rubber mallet to dislodge any broken edges onto a drop cloth. Run a putty knife through the inside edges of the window frame to ensure any debris is removed. Apply a thin layer of glazing compound evenly into the inner lip of the window frame before inserting the new pane.
Purchase some glazing points from a hardware store in order to secure the window pane inside of the frame while the glazing compound dries. To do so, maneuver the points between the window and the frame. Once the glazing compound dries, remove the glazing points.
Use a thin layer of silicone sealant around the areas where the glass touches the frame. The sealant protects the window pane from shifting and weatherproofs the window. If you live in an area that is known to have extreme weather, add a light coat of weatherproofing wood primer to the frame before preparing it for the new pane.
Always use protective gloves when working with glass. Be careful when working with tempered glass because it breaks into many small pieces. If the original pane is broken tempered glass, use a vacuum attachment to get all the pieces out of the frame, or use a putty that removes the pieces from the inner lip.