Microsoft will release the Windows 8.1 Update via Windows Update. If you're in a hurry and can't wait, the company has quietly provided download links for all the files required to install the new version.
As you can see in the list below, Microsoft has released download links for all versions of the Windows 8.1 Update. This includes installers for both 32-bit and 64-bit devices, as well as for ARM tablets, like Microsoft's Surface.
If you're not sure what order to install the files in, KB2919355 is the main package, so if you're running a fully updated Windows 8.1 system, this is the only package you need to download.
Download the updates for Windows 8.1 Update x86:
KB2919355
KB2919442
KB2932046
KB2937592
KB2938439
KB2949621-v2 (only for Windows Server 2012 R2)
Download the updates for Windows 8.1 Update x64:
KB2919355
KB2919442
KB2932046
KB2937592
KB2938439
KB2949621-v2 (Windows Server 2012 R2 only)
Download the updates for Windows 8.1 Update ARM:
KB2919355
KB2919442
KB2932046
KB2937592
KB2938439
