This plugin is for programmers and not users of WordPress. The chess board can't be enlarged. Maybe but you won't get the answer from the developer.
The board is a bit small but you can make it bigger if you go to https://code.google.com/p/pgn4web/wiki/User_Notes_wordpress and follow the directions.
It's a magnificent plugin.
You must log in to submit a review. You can also log in or register using the form near the top of this page.