Before you run the downloaded installer, make sure that you have moved the existing Lightroom 5.5 (or 5.4, 5.3, etc.) to the Trash and emptied the Trash. (Before emptying the trash, make sure that there is nothing in it that you might not want to permanently delete, of course.)
The reason for doing this is that the installer may choose to skip parts of the installation process if there is already an instance of the application in place that is deemed 'newer', for whatever reason. The installer may also update a different instance of Lightroom 5 than you expect, if you have several versions of Lighroom 5 installed on your system. (This is OS behavior.)
There will be messages showing up in /var/log/install.log (viewable in the Console app, if you choose 'install.log' in the log list pane) which may allow you to determine if the installer did indeed skip steps and/or did something else 'out of the norm'.