If you are logged in to your HelloSign account right now, you can visit this page to update the card on file.
You can change your credit card information by signing in and clicking on your email address in the upper right corner, then Settings from the drop down menu:
Click on Billing at the top and use the 'update' link to change your credit card information.
Note: Only team admins can change the billing information for a team. If you aren't a team admin, you will not see this option to update your team's billing information in your account.