3.x doesn't do an uninstall of the previous version. It leaves it fully in place.
It installs in a separate folder makes 3.x the default.
I would leave the old version on the PC until you given 3.x a good hard test drive and you're sure it's ready enough for you. If you hit a problem / bug that's unacceptable, you should be able to uninstall 3.x and revert back to 2.x without a lot of heartache.