BILLETS uses the native language file system for its respective Joomla! version, so changing the text of emails will vary depending on your Joomla! version.  Please refer to the appropriate instructions below.  Thanks! 

JOOMLA 1.5.X

• Download and install this free, fantastic language file manager:  http://extensions.joomla.org/component/option,com_mtree/task,viewlink/link_id,1776/Itemid,35/ to manage language definitions in a simple, graphical manner, directly from the admin-side of your Joomla! installation
• Alternatively, your can modify these two files:
• root/languages/en-GB/en-GB.com_billets.ini
• root/administrator/languages/en-GB/en-GB.com_billets.ini

JOOMLA 1.0.X

• The language file system in Joomla! isn't as well built, so we've included our own language file manager for the 1.0.x versions of our components.
• Go to BILLETS>>Languages and edit your language file(s).  You will only need to change a few constants, and we've positioned them at the top of the language file