1. Dashboard > Appearance > GeneratePress – enable Elements Module
2. Appearance > Elements > New –> Header Element.
3. Give it a Title and Add Some content, if you only want the image to be displayed then add: <!-- featured image -->
4. Set the Top and Bottom Padding to give the element some height eg. 200px each.
5. Select Background > Custom Image
In the field provided select the Image.
6. Go to the Display Rules Tab, in Location select the Front Page ( this is the Home Page).
In the Header Element, next to padding you have a Mobile icon that will allow you to adjust the mobile padding, try setting top and bottom to a % size eg. 15% top and 15% bottom. This should keep it responsive.