Go to your Account Settings, under 'My Ocado', and select Payment Details. Once you're there, locate the card that you wish to use and click the option to link the payment as the primary method for 'Ocado Reserved'.
Please note: Updating your payment method for Ocado Reserved will not automatically update orders that have already been placed, if you're needing to update any existing deliveries go to Orders under 'My Ocado' and edit your order the usual way. You'll be able to select an alternative payment method at checkout.
Need help adding a new card? Please read our FAQ, 'How do I add a card to my account?'