To change your credit card, log in to the dashboard, then go to the "Profile/billing settings" page, click the "subscription" sub-menu item on the right hand side and then press the "change card".
You will need to be the administrator, or the person who originally set up the account. Invited users ('collaborators') can't see any billing information, or update it.
It's as easy as that! You'll be redirected to a separate secure page to update the card.
If you don't have access to the administrator account but need to change the card in a hurry, just let us know and we'll be happy to send you a link.