There is an empty div in the header with a class of dgo-page-bg
which has the following background image:
.dgo-page-bg {
background: rgba(0, 0, 0, 0) url("images/home-roof-thermal.jpg") no-repeat scroll center top;
height: 440px;
}
Try adding this to your css:
.page-id-410 .dgo-page-bg {
background: rgba(0, 0, 0, 0) url("URL of desired image") no-repeat scroll center top;
}
Upload the image you want to use to your media library, and replace the “images/home-roof-thermal.jpg” with the URL of the image you want. Because you are using a more specific css rule, it should overrule the one that is loading the picture you don’t want.