If you are familiar with Microsoft Word, you should be right at home in Visio with respect to formatting text. You can format titles and text within shapes. You can also use the Format Painter command to copy formatting and paste it into another shape or text box.
To format the text, select the text box containing the text or highlight the text itself. Then, choose from the options available in the Font and Paragraph sections of the Home tab.
You can change the font, size, color, and paragraph alignment. If you want to change the font styles in a shape, just double-click the shape to select the text within the shape and change the font styles as desired.