Should I remove my old version of aperture before installing and attempting to use the new version of Aperture 3?
No, the system will update the correct files to update your old version of Aperture 3.
You should, however, repair permissions for your Library (and your system), and run "Repair Database" before upgrading. As with all data, you should never do anything without a full, verified, back-up.
Retrieving data ...