I assume you're trying to update this in BusinessObjects Enterprise....
You can do this by updating the report by connecting Crystal to BO (File|Save As, click on the Enterprise button on the bottom left.) You then need to go to the CMC and make sure that the database connection is set up correctly (user ID and password don't usually come through in this type of an update.) You'll also have to delete any recurring schedules for the report and reschedule them from scratch (using the "Reschedule" option on the instance will get you the old version of the report, not the updated one.)
-Dell