Deleting a Scheduled transaction will stop any further occurrences of it but it will not delete the transactions that were created by it.
In order to delete Scheduled transactions, please first switch to Scheduled transactions section: click on the calendar icon in the menu.
Please note that it is not possible to delete a Scheduled transaction simply by deleting the transaction it produces. Scheduled transactions are like templates that create a copy of themselves when the time is due. Once the copy is produced, the created transaction is not aware that it was created by a Scheduled transaction and therefore is completely separate from it.
Once you've switched to Scheduled transactions section, notice that your transactions are listed as little squares below the calendar. To delete a Scheduled transaction, click on the box that you wish to delete and select Delete from the contextual menu.