There is a custom content component that once added to the page can be updated via custom content in the admin. I am assuming your homepage is a different template than your other pages. You add the custom content component to the homepage template in studio (make sure you know which custom component you are adding to the page). I would recommend testing on stage, but the directions for the admin peice are the same on stage and production. In Admin under content>Custom content, put the content you want in the custom content which can be HTML and freemarker text. Not sure where you are hosting the image, but you can go about it 1 of 2 ways, either reupload the new image with the same name so the banner changes automatically, or you will need someone that knows enough html to know where to change the image name if the image upload is a different name every time in the custom content module in admin. Note, even if you put content in the staging admin custom content, you will need to readd in production since admin settings don't transfer in staging pushes. It is a clunky process and I wish Lithium would make it a little easier, but this is what we have. I did float the idea for the custom content module to be WYIWYG, but never got voted on.
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