I’m guessing you might need to format your drive and then boot a W10 ISO through BIOS to install it. I don’t have any prior experience, so take this with a grain of salt.
It’s also possible that you might be able to do a system recovery and you may have a Windows 10 image somewhere. Just make sure that you take a backup of all your user files regardless of which approach you take.
Edit: Just one more thing: official support for W10 ends next year, with your only option of extending support being a fee to extend your use of W10 by 10 years if I’m not mistaken.