Microsoft has recently released the May 2013 version to coincide with the regular release through Windows Update.
In Both Surface RT and Surface Pro to Get Firmware Updates Today, we told you that the Surface RT and Surface Pro were getting firmware updates for May 2013. These updates are distributed through Windows Update along with other operating system updates as part of Microsoft's monthly patch cycle.
If you have Surface Pros deployed in your organization and connected to your network, you'll probably want to update them using the same corporate policies you use for updating regular Windows-based endpoints.
A few weeks ago in Enterprise-ready Surface Pro Firmware and Driver Pack Available, we let you know about Microsoft providing the files for deploying updates to Surface Pro devices. Microsoft has recently released the May 2013 version to coincide with the regular release through Windows Update. This manual download allow you to control deployment of the latest firmware and drivers.
Microsoft has graciously used the exact same download page for the updated firmware and drivers, so from here on out, it looks like you can just bookmark the following to check for changes.
The download link: http://www.microsoft.com/en-us/download/details.aspx?id=38826