Locate the bolt fasteners that secure the first slat to the swing. Attach the correct socket size to the nut and rotate it counterclockwise to remove it.
Place the old slat against the replacement material. Flush up the ends of both pieces and mark the opposite ends to determine the correct slat length. Cut the new slat using a circular saw.
Equip an electric drill with an auger bit featuring the same diameter as the old slat's holes. Hold the old slat with all of its edges flush with the new material. Insert the bit into the old slat's drilled holes and drill new holes into the material.
Set the new slat onto the steel porch frame. Slip new bolt fasteners through each drilled hole and secure them by threading on nuts. Tighten the nuts using a ratchet.
Repeat the process of removing and replacing the slats until the project is finished. Secure each new slat before removing another old one to keep the steel frame intact and square.