Just to clarify...
The group windows "Name" object is a text object. One of its atributes is "Font" which references a predefined TextStyle (something like /TextStyles.Normal.NormalStyle).
You want to change that reference to point at one with a smaller font size (something like /TextStyles.Small.SmallStyle)
Double-clicking the reference will jump you to that TextStyle. You can see all the other SOE standard styles near it
There are additional TextStyles available under /Fonts but as Landiin said, these are being phased out by SOE and could be removed at some point.
As a last resort, you can add your own TextStyle. If doing this, you probably want to add it directly to the Group window unless you need to use it in other windows.