Change start up default user account

I bought an HP Pavilion floor demonstration computer from a general retailer. The salesman assured me that all previous user accounts and information had been removed and the computer restored to its factory configuration before I took delivery. However, when I boot it up from a cold (power off) start, I get an error saying that the password entered for user Kiosk is invalid. Kiosk is apparently the name of the default start up user account. My workaround is simply to switch users to the administrator account. The Kiosk account does not appear in the list of user accounts in the 'add or remove user accounts' tab in the control panel. The Kiosk file folder in the Users folder is empty. How can I change the default start up user account? The store did not create a password reset disk.

Will it log in now using the Admin account? Is this the hidden Admin account?

If you don't want to run under the hidden Admin account, can you use it to create a new User account with Admin privileges?

With the huge load of bloatware that throttles Win7 on HP's I would consider Clean Reinstalling Windows 7 Factory OEM.

Another option is to run full Factory Recovery to get a fresh start with your personal owner's User Account which often can never be fully deleted due to security precautions: HP Recover Windows 7 Operating System Using HP Recovery - HP Customer Care (United States - English)