Open the file in this path /wp-content/themes/painting/functions.php using some editor like DreamWeaver.

There you can add below code,

add_filter('woocommerce_short_description','limit_woocommerce_short_description', 10, 1); 

function limit_woocommerce_short_description($post_excerpt){

if (!is_product()) {
$pieces = explode(" ", $post_excerpt);
$post_excerpt = implode(" ", array_splice($pieces, 0, 10));
}

return $post_excerpt;
}

After that open the file in this path /wp-content/themes/painting/woocommerce/content-product.php using some editor like DreamWeaver at line number: 106 Approximately.

There you can add below code,

echo apply_filters( 'woocommerce_short_description', $post->post_excerpt );