I notice the upgrade to 4 Pro does not replace 3 Pro.
Can/should 3 Pro be uninstalled?
I currently have all versions from 2 Express to 4 Pro on the same machine. There don't seem to be any issues if you want to leave 3 installed. You can remove 3 if you wish.
You can only run one at a time, but having them all installed at the same time shouldn't be a problem.