If you feel you need to change any of the text displayed on your store then you can do so my simply editing this file on your server.

/includes/languages/english/index.php

If you need to it for another language that is already installed on your shop then simply change the "english" part of the above file path to that language name, you can see a list of all the available languages in the /includes/languages/ directory. To create a custom language file for one that isn't on the list then simply duplicate one of the existing language directories, rename it to the new language and edit the text contained within to your requirements.

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Lawrence