LabWindows/CVI 5.5 is not a free upgrade. It is a major upgrade include many, many new features. You can order an upgrade from CVI 5.0.1 to Measurement Studio 1.0 which includes CVI 5.5 form http://www.ni.com/upgrade. What you downloaded was just the new run-time engine for CVI 5.5 which CVI applications use when distributed. It's not an update to the developement environment.
Best Regards,
Chris Matthews
Measurement Studio Support Manager