To update your credit card you would just need to log into your account center ( https://www.crucialwebhost.com/account/ ) and look for the My Fiance tab at the top and click the Update CC option.

Lots of browsers will accidentally pre-fill this page with the wrong info if you have your browser set to save passwords, so you may need to remove your email address from the 'New CC Number' entry space. The password entry is just the same password you used to log into the Account center, if you have it saved in your browser there is usually somewhere within the browser settings where you can find the entry to copy / paste it. 

If you still have issues let us know by opening a ticket with the Billing Department and let us know what is happening and at which step so we can figure out the cause and assist you with updating your payment information.