How to change a 'class'

[reg at dwf.com]

I just brought up FreeBSD 10.2, and when it asked for
a class for my user account, I said 'system' rather
than 'wheel' which I assume would have been correct
to allow me to 'su' from my user account.

How do I delete 'system' and add 'wheel'?

And yes I know the simplest solution would probably
be to delete the account and do it right the first
time arround.
-- 
                                        Reg.Clemens
                                        reg at dwf.com