If you are using the vCSA over the Windows based vCenter Server, you will notice Update Manager is not available within the Appliance. This is because as of vCSA 6.0 Update 2, it is still required to have a Windows machine deployed with Update Manager.
You will need the vCenter Server (Windows) iso in order to deploy Update Manager. Also the Update Manager version needs to match the current patch level of your vCenter (This might be a good reminder to patch vCenter if you haven't!).
The installer comes with SQL Server 2012 SP2 Express, which is ok for a basic install, you can use your own SQL Server on a remote dedicated server, however you will need to ensure the .NET 3.5 Framework feature is installed. The SQL Server Express installer fails without proving a useful reason if you don't, another reason might be that you have a pending reboot. If it still fails, download the standalone version of SQL Express from the Microsoft Website which will show you the correct reason why it fails.
The .NET 3.5 Framework is is installed as a feature in Windows Server 2012 R2, however you will need the Windows Server 2012 R2 iso in order to install .NET 3.5 Framework. During the feature installation it will prompt you for the source which should be "D:\Sources\SxS" (Where D: is your DVD Drive).
Once you have the prerequisites in your Update Manager vm, you can simply just install Update Manager, point to your vCenter Server and provide credentials to access it (I provided the administrator credentials in my case).
Once the installation is complete, in the vCenter Web Client you will now see an icon for Update Manager which you can then configure as normal.