Are you sure about "Mac OS 9.0.x"? Or is it rather Mac OS 10.9.x?
If you are running MacOS 10.9 Mavericks, then Aperture 3.2 is no longer supported. Upgrade immediately to Aperture 3.4.5; you can download the installer from the Apple Support page: Aperture 3.4.5 http://support.apple.com/downloads/#Aperture%203.4.5
After running the installer, launch Aperture and enter your registration number, and then sign into the AppStore to upgrade to Aperture 3.5.1.
The App Store will convert your previous licence to an AppStore licence, bound to your AppleID, so be sure to sign into the AppStore with the AppleID you are using to buy and upgrade software.
One more thing - if you are not living in the United states - in some countries, e.g., Germany, Scandinavia, people had difficulties to find the 3.5 update at the App Store. It was necessary to set the primary lauguage to English and the region to U.S. in the System Preferences "Language&Region" panel. If you are having similar problems, try to change the language and region and reboot, before trying to open the updates page in the AppStore.