You can download C2 on Steam.
Otherwise, Check in the menu "About" window/"View license", and see where your license.txt file is located and move it in another folder. Reload C2 and hopefully you should have the free version.
It's hacky, so be careful and be sure to have a backup of your license somewhere and put it back in place once you're done.
Also, be aware that free version can open and execute any capx (even one that goes over the limits of the free version). The limitation for the free version is that they won't be able to edit a capx that goes beyond the limitations.
And you can create a capx that will be "OK" for free version simply by using no families, only one webGL effect, having less than 100 events and no more than 4 layers per layout even in a licensed version. (that's how I made most of my tutorials on gamedev tutsplus