HeatSpring Members can update the credit card number on file for the subscription. Just log into your account at https://heatspring.com/account then click the blue "View Subscription Details" link next to your membership subscription. Then click the blue "update card" link next to the card details.
Credit card transactions are processed securely with Stripe. All credit card data is passed directly to Stripe and stored in their vault and HeatSpring never stores nor sees credit card numbers.
Updating your credit card through your HeatSpring account will update the card on file in the Stripe vault to be used for the monthly subscription charges. HeatSpring will also send out notification emails if a charge to your card fails with a quick link to update the card from the email. Updating your card through either method is acceptable.