Examine the ends of the bed frame to determine if you need additional brackets. If there are no flat ends with slits running perpendicular to the frame, purchase and install footboard brackets according to manufacturer's instructions.
Remove the mattress and box spring and hold the footboard up to the end of the bed frame.
Line the slits in the brackets up to the mounting holes on the footboard.
Fit a washer onto each mounting bolt and thread the bolts through the slits on the end of the frame and into the bolt holes on the footboard. Tighten all the bolts.