The banner on your website, by default, is named 'banner.jpg'. To change or overwrite the existing image, name your new banner image "banner.jpg" and upload it in Content Upload (read how to use Content Upload here.) After the new image is uploaded, you can refresh your page and see the new banner in place. Please note that the file extension must be ".jpg" and not ".jpeg" as our system will not recognize an image titled "banner.jpeg."
The typical banner size is 1000 px wide but this can vary from site to site. To determine the size of your current banner, go to yourdomain/images/uploaded/banner/jpg (where your domain is the URL of your site, e.g. electjohndoe.com). Then right click the image and select properties, where you should see the dimensions listed.
Your banner can be any height you wish. However, if you make the new banner taller than your old one, you will need to contact Blue Utopia (firstname.lastname@example.org) and request an adjustment to your template file, as this height is set in your template.