To transfer the license to another machine, you can do two things:

1. Try to register another device and take it from there

If you try to activate another machine and you've hit the activation limit, you will be presented with a nice activation dialog. This will allow you to de-activate a certain computer — then activate the current machine.

Alternatively, you can...

2. Explicitly deactivate one computer — Then re-activate another one.

You have the option to de-activate a license on a particular machine. In the license manager click "Deactivate this Device". This will release an activation, ready for another computer to use.