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That explains why I couldn't find it anywhere lol! doh!you can find any core language entries by going to admin -> Content -> Manage languages
then search for part of the phrase.
this will let you change the wording for any of the "core" verbiage.
If its from a user contributed plugin (like this appears to be) you need to navigate into the plugins folder (using FTP or cPanel file manager) and edit the language file for that plugin manually.