I don't think you can. After all, even if you contacted an admin, they'd have no way of verifying you are actually the owner of that old account.
I'd chalk it up as a learning experience and start over with this current (or a new) author identity, then post your future stories under that. Maybe figure it's your penance for making a poor choice, if that helps you swallow the whole thing easier. And in the future, if you want to improve a story, you can simply resubmit an edited version, in case you weren't aware of that. There are instructions in the Submissions FAQ on the story side of the site.