The Format tab allows you to control the look of object symbols.
Click the Format tab of the General Settings category, to set the default horizontal and vertical size of all symbols in the diagram containing text (measured in units of 1/7200 of an inch).
For objects, click the Modify button to change the line style, fill, shadow, font, and custom shape of symbols (see Symbol Format Properties).
The Preview box displays the format of the new objects you are going to create not the format of existing objets. In the case of existing objects, only the attributes modified in the display preferences are modified in the diagram