I believe like everything Google the Nik Suite is now set to self-update by default and, as Dave said, should notify you when it does - though like many pop-ups, if you're not looking you may not catch it. Also, like all things Google, it's impossible to find information about versions and updates on their website, which is minimally informative.
That said, this suite has become so integrated in my workflow that I'd be lost without it - at least for a week or two. Dfine is an amazing noise reduction tool, Viveza virtually eliminates the need to even think about adjustment layers and masks, and Silver Efex Pro is
the best B&W converter I've ever used. I've barely scratched the surface of what I can do with Color Efex Pro after almost a year, but some of the filters have become essential to me for certain types of shots. And HDR Efex Pro is a superb tool.
It's the shizzle, ma nizzle!!
PS - If I have one complaint it's that the individual tools still suffer from a lack of cohesion in terms of what key strokes do. For example, space bar is used for 100% zooms in Color, Silver and HDR Efex, but not Viveza where I have to double-click or use the zoom tool.