Quite a few ways to do that:
1. In mintMenu, right-clicking a menu-item should give you the option of uninstalling (I'm running KDE at the moment, so I can't double-check right this minute).
2. Open Synaptic package manager (referred to in mintMenu as 'Package manager'), find what you want to remove, right-click or whatever you want and select to remove.
3. If you know the name of the package, (intermediate-expertish or generally not noobish - I don't officially recommend this approach,) you could always just open a terminal and enter 'sudo apt-get remove [package-name]'. Or with the option purge, to get rid of the configuration-files as well.
4. In the RC-version of mintInstall/Software manager, you can choose to uninstall packages as well, but since Helena isn't properly released yet, I assume you're running Gloria and have the version without this capability.
Pick your poison.
(How many other ways can we think of?)