Follow this step
sudo su -- get super user acess
passwd admin -- changing password for admin user
Update the PasswordAuthentication parameter in the /etc/ssh/sshd_config file:
PasswordAuthentication yes
4. Restart the SSH service.
For Amazon Linux, RHEL 5, and SUSE Linux, use this command:
sudo service sshd restart
For Ubuntu, use this command:
sudo service ssh restart
5. Exit the SSH client, and then log in to test the password authentication.
reference link : https://www.digitalocean.com/community/tutorials/how-to-create-a-sudo-user-on-centos-quickstart