Update from 4.2.1
Just install CComment5 over. No need to uninstall CComment 4.2.1 . CComment 5 should recognise that you are updating from version 4.2.1 and make the necessary db changes.
Unfortunately when we update we need to reset your plugin settings. That is why once you update, please navigate to Components -> CComment -> Settings and configure the settings to your liking.