Hey there, cid73g.
You can always do that if you have your Windows product key. However I'm not so sure about the downgrade. There are some solutions offered on the web: http://www.windowscentral.com/how-downgrade-windows-10-windows-7.
On the other hand, I'd recommend that you get in touch with Microsoft's customer support and ask for more info and instructions on how to do that.
Hope that helps.