To the OP, I originally went with THFoster (or thomashfoster, I can't remember) when I signed up for the site. I knew very little about caching at the time and didn't realize that this would be my handle for signing caches as well. Shortly after I started my wife fell in love with geocaching too.
I simply emailed the site and asked if they could change the screen name and explained why (TnAnConyers = Thomas + Angela. We live in Conyers, obviously). A day or so later I received an email stating that it had been changed for me.
Simple!