Default Icon Size enables you to change the default size of all new Subsystems and Modules in the diagram.
For each of the icon types click on Small, Medium, Large or Variable.
If you selected Variable, then you can choose the size of the icons using the mouse. Hold down the left mouse button and drag the slider to the required size. Release the left mouse button.
When you have finished, click on OK to make the changes or Cancel to keep the current sizes.