If you want to set up a new credit card, you can go to billing settings > payment methods and choose credit card. After you saved, you will receive an email from firstname.lastname@example.org with further instructions how to setup credit card information.
If you want to change your credit card information send an email with your company ID (this ID can be found by clicking on the account name in the top right of the tool > image 1) to email@example.com. After we have received your e-mail we will send you a link to adjust your credit card details.
Image 1: Company ID Image 2: Payment method - Credit card