[Events +] Where to customize the text of the "Information about a group event" email?

Upon creation or update of a group event the group members receive an email with subject "Information about a group event".

The standard contents are: "Dear USER_NAME, ,

An event is created/updated. I hope you will join in that event. Check the event here: EVENT_LINK"

I can't figure out how to customize this email message.
Hope you can help me.