if you look in your images folder in the Elements of SEO template you will see banner.jpg, banner1.jpg & banner2.jpg. you are using banner.jpg from the looks of your blog.
if you want a different banner with the same size it's easy. if you want a different size banner you will have to change some dimensions in the style.css file.
k, so easy way: if you have photoshop or any image editing software that you can save pictures in a jpg format just open banner.jpg up in it. make the changes you want to the image and save it as banner.jpg again. after that, upload it to the images file on your godaddy server. this will override your current paintball splat banner so if you want, you can make a copy of that one somewhere else or re-download the theme and get it later.
this is what i would do. good luck!