Go to the Software Boutique, search for and locate the applications and select the "uninstall" button.
Or, open a terminal and type:
sudo apt-get remove <application name>
For example:
sudo apt-get remove vlc
It is always a good idea to purge any residual files of an application as well. For example:
sudo apt-get purge vlc
When you have finished installing or removing software, it's a good idea to execute the following commands, in order:
Get rid of any dependencies no longer needed by the system:
sudo apt-get autoremove
Ensure your system has access to all of the most up to date improvments and security fixes
sudo apt-get update
Install any fixes/improvements to the system that may be available:
sudo apt-get upgrade