Once you’ve created an account there is no way to change your login. However, note that your login is only used for sign in purposes, and isn't visible publicly or to publishers.
We can delete the account if you’d like to create a new account with a different login. Just contact support and include your full name and login. However, once we delete your account, you will lose access to any books currently in your account and will need to re-request them if they’re still available.