How do I uninstall Cinnamon?

I remember something like that

sudo apt-get purge cinnamon  

In my case, I uninstalled it by the command mentioned by Enes. But I was still getting notification for updating Cinnamon.

I solved it by using these two commands:

sudo apt-get purge cinnamon
...
sudo apt-get autoremove

In order to remove cinnamon and all the related packages the PPA installed you need first to install PPA-purge: disables a PPA and reverts to official packages.

sudo apt-get install ppa-purge && sudo ppa-purge ppa:gwendal-lebihan-dev/cinnamon-stable

You can see a little example of how to use PPA-purge http://www.webupd8.org/2009/12/remove-ppa-repositories-via-command.html