Once you have created your banner, assuming the template you are using has given you that ability, there is a bit of a process to go through to get it working on your site. Make sure that your banner conforms to what the template maker has made available to you. For example, the banner area of this site's template¹  is 468 pixels wide by 60 pixels high. When I created the graphic, that is the size I made it. So, here's what to do: