Quicken gives you the flexibility to edit the details of an existing scheduled transaction. You can modify the schedule and the recurrence options.
To edit the Transaction Details select Edit All Instances, then update the details on the screen. Select Save when you are done.
To edit the Transaction Schedule select Edit All Instances, then select Schedule and make the appropriate modifications. Select Save when you are done.
You cannot change most details of a scheduled transaction without changing all transactions, but you can edit the Date and Amount without changing other transactions.