How to restart this rig

I have twice in the past "re-booted" my computer from somewhere in the BIOS (I think this is what it is called- the setup menu you enter when you are rebooting and hit "del"). This function has allowed me to restart my computer so that it is essentially restored to the original factory settings (software, etc.).

Could someone please instruct me on how to do this again? I cannot remember.

I have a Dimension XPS R---

Thanks