How do I change the main top images

How do I change the main image in Catch Everest Pro? I don't want to add a header image above, which seems straight forward to do, but I want to change the already existing images that comes with the theme. I have managed to do so on the smaller once at the bottom but for some reason it seems impossible to change the main once, i.e the photos of mount everest and the nepal prayer wheels. How do I change these to my own images? PLease help...