- Login with your email address and your password
- Click on your username (first name and the first letter of your last name)
- Click on "My account"
- Click on the symbol of the payment methods
- Update your credit card data
- Click on "confirm"
NB: please note that if you Sky subscription is paid through your Apple account, you still need to unsubscribe from iTunes/AppStore if you switch to a credit card payment: more information.