To change and view your account settings start by logging into or by Clicking the “Your Account” link at the top of this site.

After logging in you will see your remaining data and other existing account information.

On the plans page you can change your current subscription. Plan upgrade changes are effective immediately, downgrade changes will take effect on the next billing cycle. You can also cancel your downgrade from the main account page.
See information on the planspage on how data and price is calculated when changing plans in between billing periods.

You may use the same credit card as your initial sign up or change your credit card here

Alternatively instead of changing your plan you can also buy a data refill which will instantly add the purchased amount of data to your account regardless of when the purchase is made.