Within a delivery method, you have the option to change the order dispatch notification email. The current email is a default delivery despatch note, but you can use these to your advantage by using 'custom emails'. For example, if you delivered on a Saturday but only between 10:00 and 14:00, then this is specific information for the customer. You can then put all the information required for the customer in a custom email.
You can find more information on custom emails here.
To change your default email then firstly go to the back office of your website and select shipping. Under the tab 'Shipping Zones', you will see all of the shipping zones you have set up. In the third column titled 'Delivery Methods', You can see that each shipping zone has its own number of delivery methods as highlighted below.
By clicking on one the numbers you will see a list of delivery methods for that shipping zone as shown below.
By Selecting the edit pencil in the far right column under 'Actions', you will be taken to the delivery method edit page as shown below. This is where you can edit the details of the delivery method and on the third line down, you can select what type of email you wish to be sent.