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 :