riz,
That's a toughy. See the discussion
here, but the reality is something like this:
"...a user name (the name used to login with) cannot be changed. If you wish to change a name you need to reregister with a new account, advise the mod team of that reregistration, and post an open letter in the public male survivor forum advising site participants of same. Setting up and/or maintaining more than one account can be cause for suspension so please avoid any possible misunderstanding by following the above stated procedure."
Sorry there's not an easier solution. In your case it would mean posting a letter in the F&F forum but otherwise the procedure is the same.