How can I update from FCPX v.3 to v.6?

Looks like I can't update none of my genuine software I purchased through iTunes store... I get a list of updates available for my computer including FCPX, Motion 5 and Compressor 4 but when clicking on any of the available updates box from iTunes store (Apple Store) nothing happens... This is very disturbing! I've been told by Apple representative that there might be a problem with my computer... I may need to create a new session, new account that will eventually correct this problem by rewriting a new session over an old one. What's this all about? I don't quite get it! Your help will be very much appreciated. Thanks in advance!