You can only add and delete email email accounts (there is no limit to the number of email accounts you can add).
You can delete an account by following these steps:
Log into your Luna account and go to "Email accounts"
Go to "Settings"
Click on "Delete account"
Need help connecting your new email address with SMTP/IMAP? Check out this article
Adding and deleting an email is a quick settings update!
If you want to link a new account and change your login email address, you'll need to create a new one.