In case the customer has issues with the root password for his VPS, first check if the password works for the setup wizard and if this is the case you will need to ssh to the host and then enter VPS via host, after that,
Find and uncomment line #PermitRootLogin yes
After saving the configuration restart sshd service,
/etc/init.d/sshd restart
Confirm you can ssh directly to VPS after the process