You'll need to download the Ogmo Editor version 0.918. This project may not work with Ogmo Editor v2.x. The Ogmo Editor is a free and open source level editor created by Matt Thorson. It will run on Windows, Linux and OSX.
The Ogmo Editor requires Adobe Air. If you don't have Adobe Air installed, download it from Adobe's website.
Once installed, open it up and go to File > Open Project. Open the file _SuperLemonadeFactory.oep
From here you can open existing levels or create your own.