1. Go to the Billing section.
Firstly, click on the "Settings" tab on top on your account.
From the options, select the "Billing" option.
2. Update Credit Card Details.
Here you will be able to view details of the current credit card, and, if needby update details.
Visa, Mastercard and AMEX are all accepted.
Once details are saved, this card will be topped up $40 automatically each time you have used all available credit on your account.