To add or update your payment methods, click on the profile icon in the top right of your screen and select 'Billing and Payments'.
Click on the 'Payment Methods' tab. All the payment methods that have been added to your account are listed here. You can either:
Add a new payment method - click the '+Add New Payment Method' button, and choose between adding a debit/credit card or linking a PayPal account.
Delete a payment method - click the 'bin' icon on the right
Change your default payment method - select the radio button next to the payment method you want to use as default