How to completely remove application [duplicate]

Using sudo apt-get purge <package-name> will remove <package-name> and all of it's config file that are not located in "Home" (~).

You will have to remove config files in your home directory manually. Since these files are hidden you will have to press Ctrl + H to view them in Nautilus.

A good reference to look at: What is the correct way to completely remove an application?

If you mean to remove all configuration files and all after uninstalling your software then you can use Ubuntu tweak. It is a very useful tool to do lots of things in Ubuntu, especially cleaning all unnecessary things.

The software is not in the official repo. of Ubuntu, but you can install it very easily using ppa. To install the software use the following commands

sudo add-apt-repository ppa:tualatrix/ppa  
sudo apt-get update  
sudo apt-get install ubuntu-tweak

Hope this information will be helpful to you.