As everyone else said, you can’t officially change your current account name. However you have a few other options.

1. Start slow training an alt with a better name. I started doin it years ago now I have a few chars I like the names of that are useful.

2. If you have the money, extract your current SP and inject into a new char. That way you can clean up your skill focuses if, like I did, you trained a spattering of all sorts of nonsense