Set the mattress aside. Remove the two Allen bolts or screws on each end of the daybed safety rail. Place the rail out of the way.
Remove the eight screws or bolts securing the rear stationary side. There are two screws or bolts on each end at the top and bottom of the rail. Set the stationary rail aside.
Lift the mattress springs out of the mounts to remove the mattress platform. Place the two end rails aside to assemble the full-sized bed.
Attach one set of legs to each side of the taller side rail using the bolts or screws provided with the legs. This will be the headboard. Attach the other set of legs to the shorter side rail in the same manner. This will be the footboard.
Attach a bed rail to one side of the headboard, securing it by pressing down into the mounting slots until it locks. Repeat the process to attach the other rail to the opposite side of the headboard.
Attach the footboard to the bed rails in the same manner, pushing down until they lock into the slots. Place the mattress set on the bed.