Required steps to rename user and home directory
Kill all processes owned by user and log him out
# pkill -9 -u old_username
Rename user from old_username to new_username
# usermod -l new_username old_username
Rename his home directory
# usermod -d /home/new_username -m new_username
Rename the primary group
# groupmod -n new_username old_username
Verfiy the changes
# id new_username