The free upgrades ended years ago.

https://www.zdnet.com/article/microsoft-quietly-announces-end-of-last-free-windows-10-upgrades/

You can clean install windows 10 and it will work fine.

https://www.newegg.com/microsoft-windows-10-pro-64-bit-reinstall-recovery-disc-only-no-license-key-included/p/N82E16832350238

If Dell XPS 12-9Q33 does not come with optical drive afaikt so you will need to buy a usb 2.0 optical drive to F12 boot and install with secure boot OFF.

https://www.bestbuy.com/site/lg-8x-external-usb-2-0-blu-ray-disc-double-layer-dvdrw-cd-rw-disc-rewriter-black/9243009.p?skuId=9243009

As far as I know, most systems that came with Win 8 were secure boot capable..  But I don't know the specs on that system.

Win 10 keeps an online digital key so you can use the Win 10 media, which is downloadable, to do a clean install and just not enter the license key.  It will active fine if that system has already been activated.

Are you wanting to reinstall to factory configuration or just Win 10?

https://www.microsoft.com/en-us/software-download/windows10

Yep.

Free upgrade from Windows 8 to Windows 10 still available.

Use Media Creation Tool to create bootable USB.

Upgraded from Windows 7 to Windows 10 last month on an Acer laptop.

Clean installed Windows 10 on a Lenovo that had Windows 8 DPK but wiped hard drive.

.

Thanks for all the tips, it's appreciated.