Windows 8 was the first version of Windows that I upgraded and I didn't preform a clean install. I utilized Microsoft's online upgrade offer that allowed you to install the upgraded version of the OS over the Internet.
The only problem with this option was I didn't get a copy of the media. I at least wanted a copy of the ISO file (a file that contains a image of the CD or DVD that can be burned to a physical disk with the right optical drive and media) so I can make a DVD if I need to.
If you want to download the Windows ISO, go to the following page (Upgrade to Windows 8 with only a product key). Press the Install Windows 8 button on the web page, and download the Installer.
Make sure to have your Windows 8 product key ready, enter the information into the field and then press the Next button. The application will display the version of Windows that your eligible to download, and press the Next button.
After a few minutes of downloading and processing files, the installer will ask you how you want to install the OS. Select the Install by creating media option, and then press the Next button. Select the ISO file option, and then press the Save button.