Thanks for your reply and I tried your suggestion but I still can't see where to change my credit card details.
Clicking on "Buy Licenses" takes me to a page titled "Products Licensing and Pricing" where it appears I'm no longer signed in as I can see a "Sign In" link at top right, and clicking on this takes me back to the CloudBerry Central portal.
Clicking on "Buy Maintenance" takes me to a page where I can buy a maintenance plan, which I don't want to do, but still no where to change credit card information.
It seems very strange that this is so hard to find.