Today Microsoft has released a beta version or Consumer Preview version of its next OS, Windows 8, this is not a sable version and its only for testing purpose.
You can download an EXE file from HERE, and run it, then it will tell you which version is right for you and can work with your apps which you had.
You can also download ISO version from below link and then mount it or burn on your disk to install it, or you can mount it on USB too.
You can only upgrade from Windows 7, if you wanna upgrade from Windows XP or Windows 8 Developer Preview only your user account and files will be kept but if you upgrade from Windows Vista User Account And Files, And Windows Setting will be kept for you.
Do check FAQ of Windows 8 Consumer Preview section to know more about this release.