You need to email the ed and request a change of your user name but you want to use the same email addy. The ed will let you know when the change is effective from.
I think we should be able to be unregistered on request, otherwise the other account still stands with the original name, and even if we use a different email address then it is still bad that that the old account should coexist. I asked days ago now and it hasn't been deleted.