2.0.0 replaces all previous versions, so the general recommendation would be to uninstall all previous versions. The uninstalls will leave behind any third-party plug-ins you have in the Audacity “Plug-Ins” folder, but you can copy those to the “Plug-Ins” folder in the new installation of 2.0.0.
2.0.0 has some good fixes for crashes or silenced audio when working with MP3, WAV or AIFF. It is strongly recommended you use 2.0.0.