If your Lytro account has been assigned a default username (it will be something generic like "lyt-user1234567890"), then you are allowed to change it once to something more personal and meaningful. (From Lytro Web, you can do this at the top of the screen when you are signed in to your own account.)
However, once you have selected your new username, that's it. In order to create a community that encourages civility, stability, and accountability, we do not allow further changes to usernames.
We know there can be legit and reasonable reasons for wanting a new username, especially when you're just starting out as a light field photographer (like a typo). Therefore, we do not currently put any limitations on when you can create a new Lytro account.
If you have to create a new account, you can just upload your existing living pictures to that new account.
We hope you see that we're looking out for the greater good here.