After the old panel was out I cleaned inside the frame. You will probably have some old, hardened window putty ore similar in there. I then tested the unit to make sure it is a good fit. The panes were fitted from the outside. I squirted a clear silicon bead onto the inside edge of the frame and you want to use some form of spacer under the pane to even it out in the frame. Then squirt another bead of clear silicon around the pane and fit the old wooden beads and bed them into the silicon too. Next pane same procedure. At the end I would still seal between glass and wooden bead to create a run off for the water.