* To install or reinstall Audacity, drag the "Audacity.app" icon in the
   DMG window to the /Applications folder icon on the right. Alternatively,
   drag the "Audacity.app" icon to any other location of your choosing. 

* Do not double-click the "Audacity" icon in the DMG to launch Audacity 
   from there. 
   
* If you still have an "Audacity" installation folder for a version before 
   2.1.3, you will see working duplicates of Audacity's shipped Nyquist
   plug-ins in the Generate, Effect or Analyze Menu. You may also see 
   non-working duplicates of other previously shipped plug-ins. To clean
   up the duplicates please see:
   http://manual.audacityteam.org/man/installing_and_updating_audacity_on_mac_os_x.html .