If you want to update you billing details, open up the agency settings by clicking the menu button and then "Agency".
If you want to connect the billing to a specific email address, make sure to update the email in the general agency settings. All the billing will then be processed with this email address.
By clicking "Plan & Pricing" you get to the payment, plan and pricing options.
On the left side you can see the overview of your plan. This sums up how much you pay for which service.
On the left side you can update your payment method. This is where you add your credit card details.
Under "Payment History" you have an overview which bills you already paid or are pending.
You also have the option to change your default monthly plan to the yearly plan. Depending on your plan you will safe up to 20%
By clicking "Switch to Yearly Plan" the conditions and your savings will be displayed.