If you want to change your payment method, you must first cancel your current subscription.
If you subscribed via debit/credit card or PayPal, you could cancel it within your Account in the app.
If your subscription was made through App Store or Google Play, please ensure it is cancelled within your Apple or Google account.
You can learn more about the process of cancelling here.
Once your current billing cycle expires, you must redo the quiz again on the website or in the app and subscribe with a new preferred payment method.