I've said it before, the way I do it with every new OS, is basically create an extra partition on my HDD and install the new OS there while DUAL booting with the older OS.
In this case my laptop dual boots with Windows 7 / Windows 8, and I performed I CLEAN, fresh install ow WIndows 8 on the second partition.
I never, never directly upgraded to a newer OS overwriting everything on the older one, you might end up with compatibility issues on a few programs, and it would be very difficult to revert the changes ( short of reformatting ) in case you are not happy with the new OS.
Dual boot is perfect, you get to use Windows 8 and see how you like it, at the same time you have access to Windows 7 and all the programs / games you have already installed and perfectly working on it.
Slowly proceed by installing new games / application on the newer OS and over time, little by little, you' ll find yourself having little to no reason to boot into Windows 7 anymore.......then you can proceed to further shrink the Windows 7 partition, since you mostly will use Windows 8 by now, or completely remove it......
I've been doing this game since XP / Vista days.....
