To get your forum name changed, you're required to donate. Although doubtful, you may be able to get your name changed since you have no posts. I'd just create a new forum account though, if I were you.
Forum username changes require a donation of £2 I believe for a one-time change. However as Codac said, as you've just created the account and have no posts, because of this you may be able to ask management for a free one here viewforum.php?f=897