By default the login username is expected to be an email address followed by the password. Normally the email address you used while signed up a new account or used installing the script is considered as login username.
By default , the Admin / Root log are located at http://www.yourDomainName.com/Administrator/login shows as follows :
In case you can’t recall your password please click the link “Forgot Password?” below and type your email address to retrieve your password back to your email address. The system resets old password and send back to your email.