As we've covered a bunch here at WindowsITPro, the 1st update to Windows 8.1 will release through Windows Update on April 8, 2014 as part of Microsoft's regularly scheduled Patch Tuesday. This update is extremely important in that, unless an organization installs it prior to April's Patch Tuesday, no further security updates will be offered. Microsoft has also stated that Update 1 should be treated as any other security update and follow recommended guidelines and corporate policy for updating quickly.
Update 1 requires a dependency (KB2919442) before installing. Once available the update will be labeled as KB2919355. Organizations using WSUS, Windows Intune, or System Center Configuration Manager to update systems can just approve or deploy it. There is a manual way of installing the update for those downloading early from MSDN and TechNet (yes, TechNet), but I'd just wait until it's available as a smooth update through Windows Update and connected services.
But, what about those companies that depend on created computer images for deploying or upgrading systems?
On April 14, 2014, the Windows 8.1 ISO will be updated with the Update 1 bits and made available for download from Microsoft's Volume License Service Center. The updated ISO will replace the one originally made available to VLSC in October 2013.
Windows 8.1 Update 1 is a cumulative update, so the new ISO should be used to replace the one stored for image creation now. Instead of just updating your current images with the separate files delivering on April 8, Microsoft is recommending a full swap. Just use the new ISO.