virtualbox.org

I installed 5 but whenever I reboot my Mac and Vagrant up it boots 4.3. I'm a little afraid to use the uninstall tool because I don't want to lose my machines. Any suggestions?

I don't see how that is possible since the new install of VirtualBox would overwrite the old version. The VirtualBox_Uninstall tool will not touch any guests. My one suggestion is make sure your guests and anything else that is important to you on your computer is backed up.