Why upgrade? Home does everything you need unless you require corporate network access and then I'd use Professional. Now if you have the ram going from x86 to x64 makes more sense.
Hi iva - If after checking out the comparison chart that baughman92 linked you to you decide to upgrade to Windows 7 Ultimate, I recommend doing so by using your Anytime Upgrade. It allows you to upgrade in as little as 10 minutes while keeping your files, programs, and settings intact - http://windows.microsoft.com/en-us/windows7/products/windows-anytime-upgrade