The template package uses PHP Mobile Detect to serve up the optimized layout based on device. If you are on a Desktop, you can also view the site in the Tablet Layout. Clicking on Mobile layout shows how the site will look on a mobile device. Click on Desktop view to switch back to the Desktop view.

This text is located in the file at: /languages/english/html_includes/YOUR_TEMPLATE/define_main_page.php

You can quickly edit this content (and remove this image) via Admin->Tools->Define Pages Editor, and select define_main_page from the pulldown.

NOTE: Always backup the files in /languages/english/html_includes/your_template