I can't figure out how to update my mac OS

Where is the update? It's not there when I click on the Apple App store.

I'm using OS 10.9.5 and I suspect it's causing me a heap of problems.

And my greatest fear is that my Macbook Pro laptop is 2009. I've taken great care of it, but will it not even support the newer OSs? Is there a work-around?

Thanks to anyone who truly helps solve my problem here!