I too am trying to install Windows 10 but on a brand new SSD in my Samsung Laptop. The Laptop does have Windows 8.1 on it at present. I have though removed the existing SSD with that Windows 8.1 on it and replaced that SSD with a brand new one. However, when I use the Microsoft supplied Windows 10 Pro 64 bit installation , plus tell UEFI to use the DVD Drive as first drive, Windows 10 will not install. I see the initial Windows LOGO and then it hangs. Laptop meets the Windows 10 Specifications; it has a dual core i5 CPU and 8GB of RAM.
As far as cleaning an existing drive goes, Spotted Dog could try using CMD and Drivepart, latter comes with Windows. Spotted Dog would need to read up on Drivepart first though, as it isn't the easiest of programs to use. It does have an help option but it is best to look online to see how how to use it.