You'll need to locate the Machinarium.sol file.
For Mac users, the file path is:
{YourHomeFolder}/Library/Preferences/Macromedia/Flash Player/#SharedObjects/{RandomSequenceOfLettersAndNumbers}/localhost/
{PathToYourMachinariumInstallDirectory}/Machinarium.app/Machinarium.solFor Mac Steam, the file path is:
{YourHomeFolder}/Library/Preferences/Macromedia/Flash Player/#SharedObjects/{RandomSequenceOfLettersAndNumbers}/localhost/
Users/{YourHomeFolder}/Library/Application Support/Steam/SteamApps/common/machinarium/Machinarium.app/Machinarium.solNote that the user's Library folder is hidden from view by default in Mac OS 10.7 (Lion) and above. If you're using 10.7 or above, this link will tell you how to find (or unhide) your Library folder:
http://reviews.cnet.com/8301-13727_7-20082044-263/os-x-lion-where-did-my-library-go/Edit: Seems the link above is gone, so here's a newer one:
https://osxdaily.com/2016/12/12/show-user-library-folder-macos-sierra/1. Once you've navigated to the Machinarium.app* file that is nested within your localhost folder, you will need to Control-click on it and then choose "Show Package Contents" in order to see the hidden/invisible Machinarium.sol file.
2. Simply replace the Machinarium.sol file with the one that you've downloaded and you'll be all set.
* Note that this is separate from the Machinarium application that's in your Machinarium folder.
Also, for those who might not be aware, Mac OS X comes factory-set to hide most file name extensions, so you'll only be seeing the .app file name extension if you've chosen Finder→Preferences and turned on "Show all file extensions."