Upgrade Windows Guides
Introduction
You like the way you have setup Windows Vista or 7 then why not just upgrade it to Windows 8. If it works and goes through smoothly then you should have (In theory) the exact same programs and configuration as the previous version of Windows.
Many times though I have seen upgrades go drastically wrong due hardware/corrupted files/incompatible software/viruses/spyware etc etc, causing great disappointment to the person involved in the upgrade and sometimes a loss of data and personal information.
It saves time setting up Windows again.
It has many issues with incompatibility.
If available run the Windows upgrade advisor first. Located here
So to sum up, if at all possible do a clean fresh install on a new hard drive rather than upgrade, this will give your computer a jump start in the world with a bright and shinny new Windows 8 Operating System.
The advantages/disadvantages, and different ways to install windows are covered more in depth here. The full step by step guides can be found here:
Windows Upgrade Guides
Upgrade to Windows 10Windows 7 Upgrade Guide (All Versions)
Older Windows Guides