If you have the advanced portal activated, and allow constituents to update pledge information, a constituent can add a payment method to their account and identify it for future pledge payments. This will not affect payments that were due greater than 30 days in the past.
Constituent can also provide you with their credit card number which can be added to their Payment Methods tab and then selected for future pledge payments. You can also record a one time pledge payment via a credit card internally using the Add Gift, selecting Pledge Payment as the Type, then selecting Credit Card as the Payment Type.
You also have the option of sending constituents a link to update their credit card information from the Payment Options tab. You can set up notifications to alert you when the card has been added/updated via the View Update Link button.