We've heard your feedback and know there are many reasons why you'd want to change your username. That is why we're already working on implementing this feature!
As for now, while this option is unavailable for security reasons, you can delete your old account and create a new one. We reserve this option for cases when, for example, your username contains your real name, which has been changed. During the sign-up, you'll be able to pick a username you like (unless you sign in via Social Media).
Before deleting your account, please make sure to contact us so we could save your membership.