Remove User Account of Pi

It is wise to make pi account disabled.

1) Add new user 'adduser'
2) Check current group 'pi' is included by 'groups pi'
3) Add new user to the groups above 'sudo adduser (new) (group)'
4) Kill all pi processes --- by default, Xserver is running so change setting from 'raspi-config'
5) Delete pi --- 'sudo deluser pi'