Since you say "crystal management console", I assume you're on some version of CE and not BO XI. I'm not that familiar with CE as we moved from Seagate Info 7.5 directly to BO XI.
However, BO XI is supposed to be similar to CE 10. To do this sort of thing, I pull up the report object in InfoView (you can't get to the scheduling info for a previously scheduled object in the CMC) and click on History. On the "instance" that's marked as "Recurring", click on the "Reschedule" link and modify what needs to be changed, and then click on "Schedule".
-Dell
A computer only does what you actually told it to do - not what you thought you told it to do.