NOTE - THIS IS 7.0 .... FOR 7.1 IT IS DIFFERENT
ON THAT PAGE YOU REFERENCE, YOU CAN CLICK WHERE IT SAYS 7.0 AND IT HAS THE SAME AS I HAVE BELOW
I think it is template dependent but here is how I do it...
Open one of the products that has Related Products turned on
While open, select Design/Site Styles
Click on one of the Products being displayed in the Related Products
It should offer you options:
Items per row .... Item spacing.... etc.
Screenshot attached