If you've already upgraded or installed Windows 10 and want to do a clean installed:
Go to Settings, Update&Security, Recovery. Under the top section "Reset this PC" click "Get Started". Then opt to not keep anything upon restoring the unit.
If you have another version that is NOT Windows 10, you'll need to download the Microsoft Windows Media Creation Tool. Or obtain the ISO. Have your Windows Product key handy. It's a sticker on your computer somewhere (bottom, side, top, back). Or use the Magical Jellybean Key Finder. Note the version just in case. Run the Windows 10 tool and upgrade your unit, keeping everything. This will register your current Windows version key with Microsoft. Once Windows 10 is installed, follow above option for clean install. The Media Creation tool include the pro version.
You should really make a new Microsoft Account if you have not done so already. Preferably a brand new Outlook.com email account, OR create an alias for your existing account with the oulook.com domain. This can be done via the web on your MS Account page.
Some computers did not get the upgrade option yet to Windows 10 because drivers are still being developed. You can try using the Media Creation tool to leapfrog to Win10, but drivers may not be available for your specific computer. Even if you got the upgrade to Win10 option, drivers can still cause issues. Those are not Microsoft issues, but manufacturer. I'd go to your device Manufacturer website and download all drivers for your device and save to flash drive first, then install Win10. If drivers are needed, just install from your flash drive. Most important is your network drivers. Once you're online, you can download the rest.