Sounds to me like you are asking the question to the wrong place.
If you used an automated installer from a third party and it did not ask you to create your account, then you would need to consult the third party as to what the username and password are that were created. No one here would be able to tell you what that is.
If you are knowledgeable in MySQL (and or the use of a SQL browser like myphpadmin in something like CPanel) you could also look at the database directly to get the username and reset the password.
- open the databse
- look at the ost_staff table
- find the first user (usuyally staff_id 1)
you can use the id or the username to update the password by running a sql query.
Using the staff_id
update ost_staff set passwd = md5('yournewpassword') where staff_id='1';
Using the username
update ost_staff set passwd = md5('yournewpassword') where username='admin';