change post exceprt default length

add_filter( 'jnews_module_excerpt', 'change_default_excerpt_length', 99, 4 );

function change_default_excerpt_length( $excerpt, $post_id, $excerpt_lenth, $except_more ) {

    if ( 20 === $excerpt_lenth ) {
        $post    = get_post( $post_id );
        $excerpt = $post->post_excerpt;

        if ( empty( $excerpt ) ) {
            $excerpt = $post->post_content;
        }

        $excerpt = preg_replace( '/\[[^\]]+\]/', '', $excerpt );
        $excerpt = wp_trim_words( $excerpt, 50, $except_more );  /* change 50 as you want */
    }
    return $excerpt;
}