Forum user/display name questions

When I created my account I didn’t realize the usernames would be static, so I went with my first character’s name, but as I now have two characters that could get confusing.

Is it possible to alter usernames?

Related, I’ve changed my name on the user profile page to Kayden Red, but it still shows up on posts as Isadora Sobeck. Is this display name setting located elsewhere? Can I change it? Do I need an admin to change it?