If you want to add some new casing to your sidelight window, then you need to first take careful measurements of the old casing, and ensure that you get some that is similar, if not exactly the same. Casing installed on the outside of buildings, such as that around a sidelight window, can ensure that the window is securely in place, and you can also keep out unpleasant weather at the same time.
Remove the Old Casing
You should begin by removing the old casing. Use your screwdriver to remove all of the nails around the casing, and then pull it away from the wall using the claw side of your hammer. The siding should be easy to remove once the screws are gone.
Add the New Casing
Begin by cutting down the casing to the right size, using your saw. Add the casing, beginning at the top of your sidelight window. Screw this into place, and then miter the end. Miter the side piece until you have a suitable corner, and then install this. Repeat for the other sides of the sidelight window. You should then add a layer of caulk around the edge of the casing.