add_filter( 'woocommerce_single_product_carousel_options', 'sf_update_woo_flexslider_options' );
/** 
 * Filer WooCommerce Flexslider options - Add Navigation Arrows
 */
function sf_update_woo_flexslider_options( $options ) {

    $options['directionNav'] = true;

    return $options;
}