Installing Standard Edition Server Updates
To apply the latest cumulative updates to a Standard Edition Server, all you need to do is run LyncServerUpdateInstaller.exe and click on Install Updates:
Once the updates have been installed, restart the server if prompted and then skip to the "Installing Lync Database Updates" at the bottom of this article.
Installing Enterprise Edition Pool Front End Server Updates
With the release of the Lync Server 2013 Cumulative Updates, the process for updating Front End Servers in an Enterprise Edition Pool has changed slightly. Most of the changes have to do with the move to using Windows Fabric to replicate data between the Front End Servers in an Enterprise Edition Pool. With the introduction of Windows Fabric a couple of other concepts were also introduced, User Groups and Upgrade Domains. Both are created and managed by Windows Fabric automatically. You can read more about these new features in the Lync Server 2013: Windows Fabric & User Groups blog post. Now because of these new concepts in Lync Server 2013, you will need to update your Front End Servers one at a time in order to make sure that you maintain quorum and at least one copy of all of the user groups. The flow chart below, from the Upgrade or Update Front End Servers TechNet article, walks through the process:
Running Get-CsPoolUpgradeReadinessState should return something similar to the following output:
If the cmdlet returns True for IsReadyForUpgrade for the server you are going to update, you can then run LyncServerUpdateInstaller.exe and apply the necessary updates on the Front End Server:
Once the updates have been installed, restart the server if prompted and then skip to the "Installing Lync Database Updates" at the bottom of this article.
Installing Lync Database Updates
You also need to pay close attention to the "Update the database after the installation" section in KB2809243. Make sure that you apply the database update to each Standard Edition Server or Enterprise Edition Pool in your environment!
Installing Updates on Other Lync Server 2013 Servers
To apply the latest cumulative updates on other Lync Server 2013 servers in your environment, just run LyncServerUpdateInstaller.exe and click on Install Updates.