Login to your account at https://my.travelingmailbox.com. Click Billing at the top right > Subscriptions > Then View on your active subscription. Then click the Change Payment Button.

This will update the card we use for your subscription only.

Note: If your subscription is on hold due to a failed payment, there will be a blue Billing button upon logging in to https://my.travelingmailbox.com. Click that button and follow the step above. After clicking View on your Subscription, you will click the "Pay" button to reactivate your account. This will also update the credit card associated with your subscription.