The General tab of the Options dialog allows the selection of a Larger or Largest font size. These increase the size of the default font and the dialogs themselves by 25% or 50% respectively.
In addition, both the font and the font size can be changed in the Query, Answerset, and History windows. You can also temporarily increase or decrease the size within these windows by pressing the Ctrl key while spinning the mouse wheel or pressing the +/- keys.