There is not a credit card update feature for existing pledges or recurring gifts at this time in NetCommunity.  You will need to have donors create a new donation with the new credit card information and create a new schedule within The Raiser's Edge to replace the current recurring gift.

For more information on how to create a recurring gift schedule in The Raiser's Edge, please see How to create a recurring gift and recurring gift payments (KB BB7689).
For more information on how to end a recurring gift schedule in The Raiser's Edge, please see How to set or change an end date for a Recurring Gift (BB446090).