If it's an option button from the Forms toolbar, you can't change the
font size.
If it's an option button from the Control toolbox:
On the Control toolbox, click the Design mode button
Select the option button on the worksheet
On the Control toolbox, click the Properties button
In the Properties window, click in the Font property, and click
the ... button.
Change the Font size, and click OK
Close the Properties window
Click the Exit Design Mode button
