You cannot change the billing address on a sustaining gift without also updating all of the credit information for the sustaining gift.  To update the gift, go to Fundraising > Donation Management > Sustaining Gifts, search for the gift, and click the edit icon for the gift you wish to edit.  Follow the onscreen prompts and then resubmit the new gift. 

Users can also make the change through the Gift Servcie Center.  Instructions for setting that up are found in this article: BB744070.