Microsoft released Windows 8.1 Preview, which offers many changes to their latest operating system windows 8.
Processor: 1 gigahertz (GHz) or faster
RAM: 1 gigabyte (GB) (32-bit) or 2 GB (64-bit)
Free hard disk space: 16 GB (32-bit) or 20 GB (64-bit)
Graphics card: Microsoft DirectX 9 graphics device with WDDM driver
Windows RT 8.1 Preview requires that you have a PC already running Windows RT with 10 GB of free storage space.
As of now no ISO file is available for download, if you have a windows 8 installed , you can get this update via Windows Store. The official website says the ISO file will be available within one day.