I have Windows 8.1 installed (not by upgrading from 8) on my MacBook White Unibody 2010 via BootCamp. Before, I had Windows 7 installed and searching through the internet tells me that if I upgrade Mac OSX operating system I will lose everything on my Windows partition. But in order to install Windows 8.1, I had to upgrade my Mac OSX from Snow Leopard to Mavericks (Free) in which I did (thus Windows 8.1 now). By doing so I had to reinstall Windows because the old partition after upgrading the Mac OSX is practically dead.
(All of the above just tells you that I have not ever performed a Windows "upgrade" (not the clean install) whatsoever.)
As of recently I am eligible for a free Windows 10 upgrade (by having Windows 7/8/8.1 installed). But because I have never performed a Windows upgrade before on the BootCamp setup that I have, I have no idea if it would work or not. Windows 10 Technical Preview works (I haven't tried it myself but a few people did successfully install it) and will install as far as I know so I am quite confident the full version of Windows 10 is compatible but getting there is the problem.
My question is "Can I do a Windows 10 upgrade when I'm on BootCamp or do I have to reinstall a new copy of Windows every time I want a new Windows OS?"
If I don't have to reinstall a new copy then I could save about ~90GBP depending on what the Windows 10 price will be.
PS. The free Windows 10 upgrade offer is not on disc. It's downloaded and installed through Windows Update.