Hello,
If you want to add header image you can do this in Theme Options > Header settings > http://prntscr.com/dpmo6l
If you want to add image for the breadcrumbs that is more suitable in your case, then go to Theme Options > General > Breadcrumbs > upload image.
If you want to use different breadcrumbs images for some pages instead of the image that were selected in Theme Options then go to Pages > edit page > upload featured image for your page and it will appear in breadcrumbs.
Theme documentation you can find here http://xstore.helpscoutdocs.com/category/8-theme-installation
Revolution slider documentation you can find here https://www.themepunch.com/revslider-doc/slider-revolution-documentation/
Regards