$ sudo apt-get remove nmon 

Uninstall nmon including dependent package

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

$ sudo apt-get remove --auto-remove nmon 

Use Purging nmon

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

$ sudo apt-get purge nmon 

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 nmon 

See Also,