Oh...I get what you mean now.

Well since the image you want to edit is called "top_home.jpg" just save the exact image on your desktop, and then edit the parts of the image you want to change (which is everything inside the rounded rectangle?).
When you're done editing, you only have to upload the image using the same name (top_home.jpg) and everything will still be the same except for the area inside the rounded rectangle.