Hello,
To change header image on default home page, you have to go to Dashboard >> Sliders >> Click on Add New button
1. Add the slider name.
2. Add the featured image as a slider & click on publish button

Here is links in our theme documentation:
https://luzuk.com/demo/lz-restaurant/documentation/assets/images/add-new.jpg
https://luzuk.com/demo/lz-restaurant/documentation/assets/images/slider-name.jpg
https://luzuk.com/demo/lz-restaurant/documentation/assets/images/featured-img.jpg

To Change Header Image in Innerpages: You have to go to >> Dashboard >> Pages >> Click on “Add New” Button
1. Add page Title and select featured image for that page which is at right corner at bottom of page.

if you need any more help, please message us.
Thank You.