how to change name ofuser and system in ubuntu code example

Example 1: linux change username

# login as root and make sure that there are no active processes for user
usermod -l NEW_USERNAME OLD_USERNAME
# if user is running kill user w the following command
userUID=$(id -u OLD_USERNAME) && pkill -U $userUID

Example 2: change ubuntu username

# To manage every aspect of the user database, you use the usermod tool.
# To change username (it is probably best to do this without being logged in):

sudo usermod -l newUsername oldUsername
# This however, doesn't rename the home folder.
# To change home-folder, use

sudo usermod -d /home/newHomeDir -m newUsername