...JUST REMEMBER THE WINDOWS KEY ON YOUR KEYBOARD!
I started this post by mentioning the Windows Key on your keyboard and that is pretty much because if/when you install Windows 8 that will be the first thing you are going to complain about.. not having a start button (that is visible and obvious).. but the Windows Key has been around on most keyboards since Windows XP so you will most likely find yourself using it all the time. I know I do as it is a lot easier then messing around with the corners of the screen, especially when using multiple monitor displays!
As I write this I am actually (attempting) to install Windows 8 on a machine that currently is running the Release Preview Windows 8 and even though it has allowed me to start the install process, it now appears nothing is happening and most likely I will find myself performing a fresh install, or at least from windows boot and choosing 'clean' instead of the option I did select which was to keep my personal data. Knowing how easy and great the pre-release versions of Windows 8 have installed on numerous computers I have messed around with, I am pretty sure this one will go flawless once I select the option to perform the clean install.
If you are ready to make/take the plunge you can head over to Microsoft and download your version from here for the USA version or if you are in Canada you will want to go here.
Oh, by the way, if you haven't already got an off-site backup plan in place, I would highly suggest buying one and installing it first and then be sure to allow the backup to complete before the actual install of windows--just in case you do something stupid like wipe your drive and lose all of your data! Click on the banner below or this link and get the best deal at less then $4 per month for unlimited storage backup--including external USB drives attached to your computer.
I have attempted to install Windows 8 (upgrade) over the Windows 8 Preview without success. It seems to start but then just hangs. I was pretty sure this would happen so a quick install of Windows 7 boot to the very basic install completed what was necessary to perform the Windows 8 upgrade. I would also note when prompted for Windows 7 key I ignored it and de-selected the 'activate when online' option. So long as you have the product key that you purchase during your Windows 8 download, that is what will be prompted upon initial install of Windows 8, even before the download starts! Therefore any question as to whether or not you need to have a previous windows installed would be 'yes' but barely!