How to edit side menu?

Hi,

I’m very new to this. On our website, we have a side menu (http://blackrockmicro.com/neuroscience-research-projects/human-research-systems/)

Once you click on the link you need to scroll down to see it.

Does anyone know what this particular side menu is called and how I can edit it? I have found pretty much all the components of the website, but not the side bar.

Thanks,
Kian