What exactly is it you are trying to do?
If you double-click the track it brings up a properties box with the via points listed in order of creation which you can click on.
If you wish to remove a point use the eraser on the tool bar. If you want to move one then select the move tool and select the point and drag to move.
If you want to split it chose the divide tool.
If you are trying to edit a via point to enter some data, I don't think you can as they are not user-defined waypoints, you would have to add one and edit that. This should be loaded into Garmin device for the ride.