Take the box spring and mattress off the existing bed frame, and move them out of the way.
Position the headboard upright against your existing metal bed frame. Line up the mounting holes on the headboard’s bottom with the holes on the frame.
Insert the bolts through the back of the headboard holes and through the existing bed frame holes. Place one washer over each bolt, and tighten one nut over each bolt to secure the headboard to the frame.
Attach the footboard brackets to the end of the existing bed frame. Line up the holes in the brackets with the holes on the side of the bed frame, and bolt them into place. If no holes exist, mark where they need to be on the bed frame. Drill through the markings using a high-carbon bit for metal.
Line up the footboard with the ends of the footboard brackets. Insert the bolts through the footboard holes into the footboard bracket. Add the washers and nuts, and tighten, as with the headboard.
Position the bed frame at your desired location, and put the box spring and mattress back in place.