How to have free and pro simultaneously at same machine?

Currently, I’m using unity 5 pro for work purposes and I need alongside it 4.6 free for educational team projects.
How do I handle having these two different licences simultaneously on the same mac?
I have installed both on separate folders, but the 4.6 free finds the existing pro licence - can I downgrade just that separately?

Use a different user on your computer for each license,