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".

How can I adjust the height of the slideshow ?

The options inside the slideshow module to change the height are disabled with this template.

You must use the options in Template manager, section "General". Here, you can choose when the slideshow will be under the Content box and its height.