You can find your current payment methods in section Settings > Billing information in section Payment methods.
You will see your current payment method which you can delete by clicking on the Thrash icon.
If you want to add a new payment method, you can just simply click on the orange button Add new payment method.
When you add new payment method, it will be used for all active subscriptions and set as your default payment method.
If you have any questions, please contact us on email or use chat in the right bottom corner.