Some of us may have not updated Aperture since Yosemite or skipped the Yosemite update, this article is for you.
If you upgraded to El Capitan or Yosemite and still has Aperture of version earlier than 3.6. You will realise that it is not possible to open the app and attempting to update result in a failure. Fear not, MacRiot has outlined the steps to updating Aperture and I will like to share it with everyone here.
Step 1) Drag Aperture to Trash but DO NOT empty the Trash
Step 2) Launch the App Store, Go to the Purchase tab and look for Aperture and click install
Step 3) After installing run Aperture to check if it is working fine. If it is fine, it is now safe to empty the Trash
Credit to MacRiot