With the options in template manager you can easily display a single background image.
If you want display a slideshow, I recommend you to install my free responsive slideshow and use the module position "image".
With my slideshow you can choose a specific height for desktop, tablets and / or phones. In this example, I choose :
- for Desktop : Height = 100% of the viewport
- for Tablets : Height = 440 pixels
- for Phones : Heigth = 360 pixels