How can I modify a Woocommerce shipping label

I am creating a Wordpress Woocommerce site. I need to have the International Flat Rate Shipping say "Call Us For Rates" instead of "International Shipping (Free)". The only value that I can change on the admin side that updates this text is to add a price. There is no way to add a label or change the price or free to text.

Can anyone suggest a way to do this?

via Chebli Mohamed