function change_role_name() {
    global $wp_roles;

    if ( ! isset( $wp_roles ) )
        $wp_roles = new WP_Roles();
    $wp_roles->roles['wpcargo_employee']['name'] = 'WPCargo Branch Manager';

    // you can also use this code
   // $wp_roles->role_names['administrator'] = 'Owner';  
    //$wp_roles->roles['wpcargo_branch_manager']['name'] = 'WPCargo Employee';         
}
add_action('init', 'change_role_name');