You can update your payment card details at any time by clicking the 'Change or update payment card' link in your original order confirmation email. 

If you have already missed a payment, you will have time to attempt the payment again or provide new card details. You will automatically receive an email titled 'Action required - Your payment failed' which contains a link to provide new card details or try charging your existing card again. You will usually have until bookings for the event close to make payment for any in arrears payment plans.