You can update your card details through CHI interface:
Go Login to your account at https://chi.uk2.net/
Login into your account:
Go to the account section, this will be in the bottom left of the new screen
Inside the admin section you need to go to the Payments & Billing tab
Inside the Payments & Billing tab you have the option to Add Credit Card (or Debit Cards) or to Add Direct Debit.