If you've created a bootable flash drive, or set of DVDs, boot the system with the drive connected.  You'll see you can boot the system from it (F12 at powerup) and once you do that you can do the restore.

Once you have a recovery drive or set of discs ready, you can restore the system to its as-shipped state even if you've altered the partition structure.

I have hit F12 at boot up and I get to a boot menu where my options are the following (or very similar):

UEFI Boot

      Network Boot

Other

      Setup

      Diagnostics

The setup option takes me to the BIOS menu where I cannot find system restore. The Diagnostic option takes me to a system test program. I have not found a Restore option.

I have just tried the boot menu with my restore disk inserted and no difference. Perhaps my restore disk is not working correctly. Are there any known issues with restore disks? Can I test my restore disk somehow?

Thanks. This video answers my questions. I should have secure boot disabled and legacy mode turned on.

Thanks again.