Use the Font Class to set the control's font and styles.
Try Font Constructor (String, Single)
Label lab = new Label();
lab.Text ="Font Bold at 24";
lab.Font = new Font("Arial", 20);
or
lab.Font = new Font(FontFamily.GenericSansSerif,
12.0F, FontStyle.Bold);
To get installed fonts refer this - .NET System.Drawing.Font - Get Available Sizes and Styles