Where do I contact weeworld? Do they pick the username for you? What are my chances? etc. Thank you."

It's definitely possible to have your username changed if there are valid safety concerns regarding your current username.  Depending on the concern in question (ie: your username contains private information, such as your full name) you have a good chance of having it changed, and they allow you to pick your new username (make sure to include it in your message to them).

You can find various ways to contact WeeWorld here: How to: Contact WeeWorld

The most effective way would be to contact them via the email address you signed up with, by sending them an email to crm@weeworld.com.