OS X :: Reset Administrator Password - Root Changes

I just bought a used Emac running 10.3.9. The previous owner does not remember the administrator password nor did I realize how important it is to have. I have the original install discs and did boot using the disc. I then went under the install menu and chose reset password. I changed the user password but have been unsuccessful at changing the admin password. The drop down menu in password reset gave me the option of Administrator (root), Application, or finally user. I have read a couple of articles cautioning not to change or work with root changes.