If your billing address has changed or you need to update the card you have on file for your account, log into your account at https://app.gopassage.com/users/edit (or go to Account -> Account). Then, click the "Billing Info" link towards the bottom of the page.
On the next page you can remove or add cards under the PAYMENT METHODS section. To remove a card click the "…" icon next to the card, and select remove. Note: if you only have 1 default card on file, you will need to add the new card first before removing the old card.
If you've moved and need to update your billing address, click "Update information" link under the BILLING INFORMATION section. That will load a form to enter the country of origin (note: you must manually select the country in order to save), city, state, and billing zip code. When all fields are filled out (including country select), hit the Save button to update.