how to disable single click with mouse to open files

I recently upgraded to Sierra 10.12.6 and I've noticed that when I try to select a file with a single mouse click it opens it instead. It used to be a double click with the mouse to open a file. What changed this and how do I change it back? It is very annoying! I cannot select a file to view the info without it opening up the software program!

I'm using a Kensington trackball mouse but it is not new. I've been using it for more than a year!