To change the platforms overall design and looks, options below can be modified from the admin panel;
-Website Icons, Backgrounds and Images (Sprite)
From the admin panel, find Design -> Theme Settings
From the top right corner of the page you can download the theme pack by pressing the Download Theme Package.
Images organized in regards to the respectful areas are added in to segments,
Header Background: Header image is uploaded here.
Logo: Logo images are uploaded here
Footer Bottom Background: Footer images are uploaded here.
Sprite: Sprite packages are uploaded here.
Custom CSS: Custom CSS files are uploaded here.