Click on 'Settings' in the left hand navigation.
Click on 'Billing Information'
On this page you will be able to view your plan details, enter a Coupon Code (if available), update your payment information and view a history of your payments.
View and upgrade your Plan under 'My Plan'.
If available to you enter a Coupon Code to cover the cost of your payment and click on 'Apply'.
To update your Payment Information enter your Card Number, Expiration Date and CVC and click on 'Update Payment Information'.
To view your Invoices click on 'View' next to the invoice date.