How to change the link of the wordpress logo in the admin bar?

You should add the following to your functions.php, you can add, edit or delete items to your desire.

remove_action( 'admin_bar_menu', 'wp_admin_bar_wp_menu', 10 );
add_action( 'admin_bar_menu', 'my_admin_bar_wp_menu', 10 );

    function my_admin_bar_wp_menu( $wp_admin_bar ) {
    $wp_admin_bar->add_menu( array(
        'id'    => 'wp-logo',
        'title' => '<span class="ab-icon"></span>',
        'href'  => 'http://yourdomain.com',
        'meta'  => array(
            'title' => __('About my website'),
        ),
    ) );

    if ( is_user_logged_in() ) {
        // Add "About WordPress" link
        $wp_admin_bar->add_menu( array(
            'parent' => 'wp-logo',
            'id'     => 'about',
            'title'  => __('About WordPress'),
            'href'  => self_admin_url( 'about.php' ),
        ) );
    }

    // Add WordPress.org link
    $wp_admin_bar->add_menu( array(
        'parent'    => 'wp-logo-external',
        'id'        => 'wporg',
        'title'     => __('WordPress.org'),
        'href'      => __('http://wordpress.org/'),
    ) );

    // Add codex link
    $wp_admin_bar->add_menu( array(
        'parent'    => 'wp-logo-external',
        'id'        => 'documentation',
        'title'     => __('Documentation'),
        'href'      => __('http://codex.wordpress.org/'),
    ) );

    // Add forums link
    $wp_admin_bar->add_menu( array(
        'parent'    => 'wp-logo-external',
        'id'        => 'support-forums',
        'title'     => __('Support Forums'),
        'href'      => __('http://wordpress.org/support/'),
    ) );

    // Add feedback link
    $wp_admin_bar->add_menu( array(
        'parent'    => 'wp-logo-external',
        'id'        => 'feedback',
        'title'     => __('Feedback'),
        'href'      => __('http://wordpress.org/support/forum/requests-and-feedback'),
    ) );
}

Hope this helps.