I see lot of football balls on GrabCAD, but all of them are designed in SW and from what i see non of them is really easy editable-parametric. I designed model in NX6 and there is only one parameter to change to get ball of different dimensions, it is parameter a=diameter of ball. It is connected to length of edge of 6-sided (or 5-sided) polygon that make surfaces of ball.
stp file of 281KB is just a ball with separated faces and 25cm diameter, and 1MB stp file is more realistic ball with 3d shaped faces and 22cm diameter.