you can upgrade to Windows 8 Consumer Preview from Windows Developer Preview, Windows 7,Windows Vista, or Windows XP, but you might not be able to keep all of your files, programs, and settings as posted on Windows Team blog. The following table shows what you can keep during an upgrade depending on the current version of Windows running on your PC:
But if you are using an Installation media such as DVD or bootable USB drive, and you start your PC from that media, then you will not be able to retain anything including your data. So make sure you choose the right path to installing Windows 8. If you still unsure where to download Windows 8 CP, then follow this link.