Its rather bizarre and not a little illogical.
You can 'Convert Track to Route' and then you'll find in the Route Properties dialog, the total climb. Why the same thing doesn't appear in the Track Properties dialog, I have no idea.
The total climb figure is derived from the map DEM, and not from the information embedded in the track itself - so is likely to be not all that accurate.
(Really either way its done, it is likely to be an over-estimate.)
There is a freeware utility GPS Altitude Chart
http://www.2steger.de/gac/that will do the job using what is embedded in the track, but it does require you to have Java installed.