The message under your name is called a user title.
At the moment you have the default user title, however you can change it with the custom user title.
What you need to do is click user cp (near the big wii chat banner), then click edit profile and the first box with a space in with a big message above is where you type what you want it to be. Keep it short.
Then scroll to bottem of the page and click save changes.
If you found this helpful, click the green mushroom near the bottem left corner of my post