How To Add Your Own Custom Logo In Your Wordpress Blog
This tutorial http://fourblogger.com/how-to-change-the-wordpress-logo-login-page/ explains how to change the defauly wordpress logo in wordpress admin dashboard login page with your own or custom logo image. Just a plugin does it. Upload the logo image through FTP or file manager. Then give the image path in Plugin settings. If you want to remove the logo, just deactivate and delete the plugin.