I don't see anyone who can change their username or delete their accounts on this forum. I find that your account rank newbie, it's best that you create a new account, with the username you like.
Then you should see this all VIP's member who can change their username
https://bitcointalk.org/index.php?topic=4425909.0Afaik donator (who have donated 10 btc) also can change their username. The difference only donator can't make custom title while VIP can.