The-F-Word is correct – in order for an upgrade to successfully move your system from Windows 7 Home Premium to Windows 8 Professional you would have to ensure the architecture for each version of Windows is identical. Example, you can only upgrade a 32-bit operating system to a 32-bit operating system; likewise, you can only upgrade a 64-bit operating system to a 64-bit operating system. As you can see in the Windows 8 Upgrade Paths
library article from the Springboard Series for Windows 8
page on TechNet, cross-architecture installations are not supported.
Hope this helps!
Windows Outreach Team – IT Pro