If you right click on the little white box with the little red X and click on Properties it shows:
http://www.file-upload.net/view-964374/D-Fenders.png.html
But you want some picture file like a .jpg or .png file. If I enter the above URL in my browser I get a page which has what I assume is your logo:
http://www7.file-upload.net/08.07.08/5ya1d2.png
This is the URL you should specify when you change your logo. As you'll see when you look at "my" logo
(23392) you're going to need to resize your logo.