To delete the scheduled transaction completely go to Scheduled Transactions View, choose the scheduled transaction you want to delete
and click Options - > Delete.
Please note that all transactions that were accepted before the date it was deleted will - not be deleted.
By deleting scheduled transaction you prevent it from appearing in the registry in future.
If you deleting scheduled transaction from registry view you just delete this particular transaction but it will appears again when the next scheduled period comes.
Read more about Scheduled Transactions