Updating payment details
If you go to Account, you will see the option for Payment Methods and Payment History. You can add a new card to pay for the premium trial or plan at any point, and view your payment history over the last 3 months. You only need to add payment details if you want to upgrade.
To change your payment card, select the option of Add New Card under 'Payment Details' tab. Once you have added a new payment card successfully then you will have the option to remove any alternate payment card that is no longer valid.