How can I change my user name?

You could try reporting your own post and putting the reason why as your comment.

Yes, report your OP and GNHQ will tell you what you need to do to change your user name.

Or could you just cancel your registration and reregister with your preferred user name?

Does that not cause problems if you are using the same email address, MaizieD? I seem to remember someone having difficulty with that, but could very well be wrong.

No it’s ok to cancel your registration and re-register with a new user name if you wish to.

[email protected] or
[email protected]

They will do it for you.
Easiest way