Julian that looks easy enough on the modern NUC’s
Go to this website Support Links for Intel® NUC
and select the model you purchased.
go to the Bios download section and download the cap file, which is an OS independent file.
Copy this file to a memory stick (I formatted mine Fat32 but others might work)
Turn on the NUC and Press F7 to boot to the Bios and then select it from the USB disk and go.
It takes 3 or 4 minutes and then it is updated and reboots.
Everything else seems to be Windows related.
I will check the next bit and update this entry with the results
To set legacy mode you might find this useful as I went around the houses for half an hour before finding it, P.S. You need to reboot and go back into the BIOS and enable Legacy Boot after making the changes.