Your web page is built using a template page. Inside the template page there are some token strings. For example @banner, which gets turned into banner image for the page.
You can set your own banner HTML code by setting this->banner in your config. You can even set it for each page separately by setting $this->banner in PHP inside a view file or more generally for all pages, in your config.php
To turn off the banner, set $this->banner = false