To install a locking Schlage commercial door handle set, first, remove the old handle by unscrewing the mounting screws and pulling it off. Next, insert the new handle’s latch into the edge of the door, ensuring it is oriented correctly, and secure it with screws. Then, align the interior and exterior handles, insert the spindle through the latch, and secure them with the provided screws. Finally, test the lock and handle for proper operation before closing the door.