How to remove user from being sudoer user in linux

• Find out user group identity

  $ #Syntax: id -nG {user-name}
  $ id -nG foo
  
  $ #OUTPUT:  admin foo printer audio
  

  by default admin and sudo groups are allowed to use sudo command as shown in /etc/sudoers file

• Now to remove a user from group, you have to user usermod command

  $ #Syntax: usermod -G {groupname1,groupname2,...} {username}
  $ #For example, to keep membership of foo in printer and foo groups only 
  $ #(and remove him from admin and audio groups) run this:
  $ usermod -G foo, printer foo
  $ id -nG foo
  $ #OUTPUT: foo printer
  

• finally restart sudo service

  $ service sudo restart