System Defaults is available to the Admin Role and accessible from the Setup menu, once Setup is selected you need to scroll down to the bottom of the list.
User Defaults relate to the specific user, System defaults are the system wide configurations which affect every user.
It is recommended that the original system defaults be preserved, if you’re not sure and you have a questions relating to any configuration please reach out to TPH Support. support@helpdesk.tphglobal.com