From [[http://www.microkwen.com/2008/09/16/force-apt-get-to-reinstall-config-files/]]\\
apt-get -o DPkg::options::=--force-confmiss --reinstall install <package>

Update: apt-get only reinstalls missing config files. You can use dpkg --purge <package> to remove the config files before reinstalling the package.

Also a simple trick from [[http://www.linuxquestions.org/questions/debian-26/how-do-i-get-apt-get-to-completely-uninstall-a-package-237772/|linuxquestions]]\\
''sudo dpkg --get-selections | grep deinstall > tobepurged''\\
You have to edit ''tobepurged'' to remove all the ''deinstall'' words, then\\
''cat tobepurged | xargs sudo dpkg -P''