How To Use Custom Logo instead of Text in TwentyEleven Theme ?

Open header.php and find this part:

<h1 id="site-title"><span><a>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a></span></h1>

Replace <?php bloginfo( 'name' ); ?> with the url of the logo.

Do not edit the Twenty Eleven theme. It is the default WordPress 3.2 theme and having access to an unedited version of the theme is vital when dealing with a range of site issues.

For this reason, it is recommended that you consider creating a child theme for your customisations. Once your child theme is active, we should be able to help with the customisation.

I have Written a Tutorial based on your help.

Adding Custom Logo in Twenty Eleven

Thanks