Click the icon and then click on any control point in one of the orthogonal projection views. All control points on the selected surface will be highlighted in red. Drag the mouse down to increase and up to reduce the size of the surface. Note that by default, the aspect ration is held constant.

You can restrict resizing to either the horizontal or vertical directions by holding down the 'H' key or the 'V' key respectively while dragging the mouse.

The information box (above the 3D view) displays information about the resize amount.

Switch between orthogonal projection views and continue resizing.

Release the mouse when you reach the desired size.