Logo is the image that displays at the top of your site. Site Builder allows you to make your own logo display on the site. To change the logo, go to http://yourdomain.com/admin => Config (at the top of the page). Under the Configuration tab look for the Logo option. After clicking on Upload you'll need to browse for the desired logo on your computer. Once it is uploaded, click OK. To add the logo image to your site check the box saying Replace "Website Name" with this logo
That's it! Now you know how to change the logo on your site.