To change the payment method, address, and e-mail address associated with your ShipStation subscription, follow the steps below:
Head to your Account Settings (the wrench icon in the upper right).
Next, select Account Settings and then Subscription from the sidebar on the left.
Once there, scroll down to the Billing Information section. Click Change Billing Information and change any information as necessary.
Don't forget to click Save on the popup modal when you're done!
Keep in mind that any billing issue with your carriers will need to be resolved with the carrier as the billing information in ShipStation is only tied to ShipStation.