How do I change standard text strings (eg "Add to cart")

How do I change standard text strings (eg "Add to cart")

Hi 

I'd like to be able to change some of the standard text strings in a template. Specifically I want to change the "View details" button on the product list to "Buy now", the "Add to cart" button on a product to "Add to basket", and the "View cart" button to "View basket".

I'm probably missing something obvious, but I can't see where to do this.