In order to edit your notification, please navigate to your notifications and click Edit. You can also access Edit notification button in the Show view.
You can edit all the fields in your notification. After you are satisfied with your update you can press Update.
To see how the end result of the notification will look like you can exit Edit Notification mode, find the notification you have just edited on the list and click Show or Send Test Email. Please note test mode will only show the dummy data and not real values.