To update your credit card information, or to change payers, pen the account menu in the upper right corner of the main app window and select on View account details... from the list.
You will be directed to an external browser window at store.proclaimonline.com. Navigate the menu on the left to update billing info, view current subscriptions, or review your order history.
Want to change who's paying for a subscription? Click on Subscriptions in the menu on the left side of the screen. Click the Edit subscription button beneath the product for which you wish to change payment, and either select a previously used card or Add a payment method.