Do you already have a SEPM installed? If so, just export the unmanaged package:
Installing an unmanaged Windows client
Otherwise, download the unmanaged client from https://symantec.flexnetoperations.com/ using your serial number.
Once installed you can configure the schedule to go out and get updates from Symantec LiveUpdate. Open the GUI and go to Change Settings >> Client Management Settings >> LiveUpdate. Here is where you create/edit your schedule.