$ sudo apt-get remove fail2ban 

Uninstall fail2ban including dependent package

If you would like to remove fail2ban and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove fail2ban 

Use Purging fail2ban

If you use with purge options to fail2ban package all the configuration and dependent packages will be removed.

$ sudo apt-get purge fail2ban 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove fail2ban 

See Also,