If you want to modify your credit card info during the subscription, please refer to the following few steps and you'll be able to get there.
(1) Please log in to your dashboard here: https://portal.istaging.com
(2) Click the profile photo on the top of the right corner.
(3) Click” Manage my account”
(4) Click “Billing information”
Feel free to contact iStaging customer support team anytime if you have further questions!