I upgraded Ubuntu 16.04 to 18.04, before which I installed GNOME desktop to be a bit familiar with it. Now, when I restarted my computer after the upgrade, at the login screen I have following options,

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I want to leave the version of GNOME installed with Ubuntu 18.04 by default and the Unity, and remove old version(s) of GNOME. How do I do that without breaking anything?

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