Save yourself the aggravation and buy a different bed. Check out thrift stores. Many folks are downsizing and getting rid of their bigger pieces.
Hi Carol, do you happen to have a picture of this bed that you want to make bigger?
All you can do is unattach the head and foot boards add side blocks to screw into your metal bed frame, you won't be able to use your side rails. The mattress and box spring will stick out on each side of the head and foot board several inches.
Other than that you'll have to remake new head and foot boards.
Thanks I appreciate you all taking the time to respond. I have decided to go with getting a new bed or redoing the upholstered headboard I made several years ago. Again thanks.