Now that Windows 8 is launched and available worldwide, you can upgrade from your old operating system to Windows 8, but there's a small catch. If you are upgrading to Windows 8 using the Upgrade Assistant, then by default, it will always install the version of Windows 8 that is corresponding to the currently installed version of your operating system. This means that if you are on a 32-bit version of Windows, then you will end up running a copy of Windows 8 32-bit and if you are on 64-bit, then you will end up running a copy of 64-bit version of Windows. Microsoft has made things complicated for end users who are using the Upgrade Advisor.
Microsoft has clearly mentioned that you can upgrade from 32-bit version of Windows to 64-bit version of Windows, but you can't do this using the Upgrade Assistant. Here's what Microsoft explains:
Can I upgrade from a 32-bit version of Windows to a 64-bit version of Windows 8?
Yes, but you can't do this using Upgrade Assistant. If your PC has a 64-bit capable processor (CPU) but is currently running a 32-bit version of Windows, you can install a 64-bit version of Windows 8, but you'll need to buy Windows 8 as a DVD.
You also won't be able to keep any files, settings, or apps when you upgrade from a 32-bit to a 64-bit version.
So if you're thinking to upgrade to 64-bit version of Windows 8 from any 32-bit version, then don't ever think of installing Windows 8 using the Upgrade Assistant.
You can install the 64-bit version by running the Upgrade Assistant on a 64-bit version of Windows and then burn the contents to a DVD or copy it on a flash drive.
If you are on a 32-bit version, then you will need to buy the 64-bit retail upgrade copy of Windows 8. You can also select media add-on during purchasing which includes two discs. The plus point of purchasing a retail copy is that it comes with two discs - one for 32-bit and one for 64-bit.
Now we just hope that Microsoft announces the official ISO of Windows 8 32-bit and 64-bit from Digital River. Once it’s available, you don't need the upgrade advisor and you can do a clean install.
Microsoft is making it hard for users to upgrade from 32-bit to 64-bit. The Upgrade Assistant should have an option to select the version of Windows which you want to install.