Will it ever be possible to change your username without having to make a new account? I heard that a new version of Ag is coming out but I don't know that much about it.
It is not possible to change your username without creating a new account.
Seeing as you are a new member, it would be easy just to start up a new account. You can even request that your old one be deleted via the "Contact" option on the top of the screen.
As said, AGv3 will be different when it comes to username options.
As far as deleting your account goes, we can only permanently ban your account as of now. Which means you would not be able to register with the same e-mail. This comment is in relevance to AG2