Full size bed frame with headboard can be good for a person, but can get crowded if two people need to sleep. If you love the look of your full size headboard, but want more sleeping space, buy a conversion kit that allows for a full size bed frame with headboard. The kits are fairly easy to install, and can be removed if you want to use your full size mattress again.
Take apart your bed; remove the mattress, box spring, ledges and rails. Take a look at the rails to determine how they connect to the headboard and footboard. If they attach with hooks, you need a conversion kit with hooks. Likewise, if the rails bolted, you need a conversion kit that attaches with bolts.
Buy a conversion kit full size bed frame with headboard. You can find many mattress stores or specialty clothing stores. Make sure to buy one that will adhere properly to your headboard and footboard, either by hooks or screws. Mount the drive rails to your headboard and footboard. If your track bolts, tighten them securely, without over tightening.
Find the center support rails. There is one in the middle of each rail. Swing them so that they meet in the middle, forming a long railway that stretches the width of the bed frame. Connect the two rails together with the hardware provided in your conversion kit. Adjust the side brackets so that they securely hold the spring in place.