For the image, you would have to use CSS media queries. It’s best to use my Simple CSS plugin as it allows you to add CSS to specific pages.
Then you could do this:
@media (max-width: 768px) {
.generate-content-header {
background-image: url( 'MOBILE IMAGE URL' );
}
}
As for the content, you would have to add two blocks of content into the content area:
<div class="hide-on-desktop">
Tablet/Mobile content in here
</div>
<div class="hide-on-mobile hide-on-tablet">
Desktop content in here
</div>