How to Update Credit Card Info
PayPal users: If you paid via PayPal, update your credit card information in your PayPal account at paypal.com.
Other credit card users: Those who paid via Stripe (e.g., not PayPal) can update their subscriptions on the billing settings page (Login > Account Menu > Billing Settings Submenu). Here's the direct link: https://backpackinglight.com/account/billing-settings/
If you purchased a single-payment product (like a course), the option to update credit card information is unneeded and does not display. If you purchased a subscription, then on your billing page, a Recurring Subscription Orders area will display, where you can click "update billing details" and complete the process of updating your credit card information:
Note: if there is no option to update billing details on your billing settings page, you either paid via PayPal and would update your info there, or you did not purchase a subscription and therefore do not have a reason to update your credit card info.