When on any page, simply click on the menu (burger icon) on the top-right-hand corner of the screen:
Select 'My Account':
Select 'Account' on the left-hand side of the screen:
Scroll down to where it says 'Payment Details' and click the 'Change Card' button. Follow the steps to update your card.
If you do not see a card, it means you do not have an active subscription. You should add one here.
Here you can also see your current plan details, as well as a record of your payment history.
If you have any trouble managing your account details, please get in touch here.