New
#11
OK. I'd recommend a clean install unless you have some over-riding reason not to do it. The main pain is that you'd have to reinstall and re-configure all your apps. The main benefit is that you have no unwanted crap on C and don't have to fiddle around with whittling down your current C from its current 800 GB.
A clean install would require that you have the 25 character "Product Key" (usually found on a sticker on an HP) and installation media that matches that Product Key--that could be a DVD or an ISO that you then burn to a DVD.