If you are a Bronze/Silver/Gold customer, start by going to pro.lookup.whitepages.com and logging in.
On the main page click on the 'My Account' drop-down and click 'Account Settings':
On the details page, click on the 'Edit' button underneath the 'Billing Info' category:
On the update billing page, enter the new payment info including cardholder name/zip code/credit card number/expiration date/cvv. Then click on the 'Confirm change' button and your info will be automatically updated.
If you have trouble with these instructions, you can place a New Request.
If you are an Enterprise customer, please refer to your invoice for contact information.