Under your login name, select ACCOUNT to access the billing information:
Select the BILLING option in your left side navigation.
Select the UPDATE CREDIT CARD button:
Populate the credit card information, and be sure to select the UPDATE PAYMENT INFORMATION at the end.
Select a Hosting Plan by hitting the button next to the plan of your choice.
You can add it a coupon code to discount the hosting subscription by entering it under the DISCOUNT section and select REDEEM.