How to change or remove the top logo in Joomla
The default logo at the top of your Joomla site can be easily changed or removed from the backend's Template Manager.
To do this, log in to the backend (admin panel) of your site, go to the Template Manager (Extensions>Template Manager), and click on the name of the template for which you want to change or remove the logo. On the edit page there is a panel labeled Advance Options.
If you want to remove the default logo click on the Clear button next to the Logo field. If you want to upload and insert a new logo image click on the Select button. From the Site Title and Site Description fields you can change or remove the title and description for the site. The title will only be shown if there is no logo.
You can remove or change only the logo from these options. The whole top banner can be removed or changed by modifying the code of some of the template files.
For some more information and screenshots on the topic of changing the logo read the tutorial on removing or changing the top Joomla logo.