Yoko Child Theme functions.php

<?php

add_action( 'init' , 'mh_unregister_sidebar' , 11 );

function mh_unregister_sidebar() {
        unregister_sidebar( 'sidebar-1' );
        unregister_sidebar( 'sidebar-2' );

        register_sidebar( array (
                'name' => __( 'Sidebar', 'yoko' ),
                'id' => 'sidebar-2',
                'description' => __( 'One Sidebar Only', 'yoko' ),
                'before_widget' => '<aside id="%1$s" class="widget %2$s">',
                'after_widget' => "</aside>",
                'before_title' => '<h3 class="widget-title">',
                'after_title' => '</h3>',
                )
        );

}