How can one change the size of a sun lamp in Blender 2.79? I can't seem to find out where to change the size of the sun lamp. When I look under the sun lamp properties, it only displays "Energy" instead of "Size". Can someone help me with this?
Sun light size has now been replaced by an angular size, which makes more sense for this type of light source.

You can control it from Angle property in the Object Data panel in the Properties Window.