$ sudo apt-get remove ngspice 

Uninstall ngspice including dependent package

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

$ sudo apt-get remove --auto-remove ngspice 

Use Purging ngspice

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

$ sudo apt-get purge ngspice 

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 ngspice 

See Also,