# add user with root user
$ useradd USERNAME
# or add like that
$ useradd -m USERNAME -s /bin/zsh
# add password for new user
$ passwd USERNAME
# add user to sudoers
$ chmod u+w /etc/sudoers
$ vim /etc/sudoers
root ALL=(ALL) ALL
USERNAME ALL=(ALL) ALL # new line
# login with new username and password
$ ssh USERNAME@HOSTIP
# change default shell of new user
$ chsh -s /bin/zsh
# with user in root
$ userdel USERNAME
# please make sure the files of USER already backup, then do the follow things
$ rm -rf /home/USERNAME
# remove USER from /etc/sudoers