From what I remember (haven’t used Smartware in a while) it will check for an update on its own, if the option is enabled within the program. See the Settings tab > Set Up Software and ensure “Automatically check for
WD SmartWare software updates” is checked. There is also a button on that screen to manually check for an update.
Chapter 8, Checking for Software Updates, in the Smartware User Manual explains it a bit more.
Edit to add: Back in September, I posted other software updates (My Cloud for Android, WD Sync for Windows) to the current WD My Cloud forum but the mods moved them to the WD Software & Mobile Apps | WD Software section. So I posted the update to the Smartware software to the WD Software section as well.