Changing ‘Calculate Shipping’ wording

Hello Friends. On our website when you add an item to the cart and you go to the cart page, there is a link that says ‘Calculate Shipping’ to see the shipping choices after entering city/state. I am wanting to change the wording for ‘Calculate Shipping’ but can’t seem to locate the file that contains this code. Anyone have any clues?

The page I need help with: [log in to see the link]