First, you will need to activate your E-junkie Reseller status by posting your Reseller button code to any live Web page:
http://www.e-junkie.com/ej/reseller.htm
Once you've done that, you can go to Seller Admin > Edit Profile and use the Upload Your Logo button to provide a custom logo/header graphic that will be used on your checkout pages (for payment processors which support it), E-junkie thank-you pages, E-junkie Marketplace Shop pages, and the "fallback" version of our cart that appears in a new window/tab if JavaScript is disabled.
However, that still won't replace the cart icon in our standard overlay-style cart; to accomplish that, see this page for instructions:
http://www.e-junkie.com/ej/trouble.reseller.custom-logo.htm