KB2919355 for Windows 8.1

Windows 8.1 Update for x64-based Systems

1. To start the download, click the Download button and then do one of the following, or select another language from Change Language and then click Change.
• Click Run to start the installation immediately.
• Click Save to copy the download to your computer for installation at a later time.
2. These KB's must be installed in the following order: KB2919442, KB2919355, KB2932046, KB2959977, KB2937592, KB2938439, and KB2934018.
3. KB2919442 is a prerequisite for Windows 8.1 Update and should be installed before attempting to install KB2919355

Ref: http://www.microsoft.com/en-us/download/confirmation.aspx?id=42335