Sometimes the information about the software is in the release notes where you download the software and sometimes it is in the FAQ's. Not sure which specific model you are looking for the 5.840 information for but it should be the same for them all as it added the Waypoint Management system features and menus to the units:
8/30/2011 12:00:00 AM - v5.840 Waypoint Mangement Menus added.