Its certainly not easy, but here is the jist.
When you click to install Windows 10, if you can find it, you need to download Windows 10 to a flash drive, and make sure it's large enough to hold the entire image. Then perform the upgrade from that flash drive.
After the upgrade, you would then use the same flash drive to install Windows 10, and this time you would choose to reformat.
I would suggest doing some google searching on Microsoft sites to get the process in detail.