To change the logo on the index.html, just use any HTML editor and paste the logo in. Then publish the logo to your server. (Rename example.html to index.html if you do not have a homepage.)
To change the logo in the Advertiser's section, go to the Main Config in the Admin section, and change the 'Site Logo URL' to point to the location where you have published your logo to.
(The URL must start with http:// and if you are not sure about the logo's URL, you can point the browser to your website, right-click on the logo, and select 'properties')