Changing your account information is quite easy.
All you need to do is log in to your dashboard and go to "Account" in the menu on the left.
Here you will find account information and billing information. This is also where you can change you email and password.
You are also able to change your email and assign super-users.
Remember to hit save after editing your information.
If you add a new credit card to the billing information, make sure that it is valid to avoid failed payments.