To change the payment method, address, and e-mail address associated with your ShipStation subscription (and Shipsurance charges), follow the steps below:
Head to your Account Settings (the gear 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!
If you wish you change the information associated with your Stamps.com account, you can login here to change it. 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 and Shipsurance fees.