sapichu

You need to make some changes in code plugin to change that.

Go to plugin/wp-post-series/src – postcontent.php and found this:

		return sprintf(
			/* translators: %1$d Post index, %2$d number of posts in series, %3$s series name/link */
			__( 'This is post %1$d of %2$d in the series <em>&ldquo;%3$s&rdquo;</em>', 'wp-post-series' ),
			$post_in_series + 1,
			count( $posts_in_series ),
			$series_name
		);
	}

There you can change whatever you want