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