On your front panel, select the 6 string controls.
The third button to the right of the Application Font selector is called "Resize Objects", select it.
Choose "Set Width & Height".
It will show you the current values for the string controls that you selected (at the bottom of the window). Pick the size you prefer and enter it at the top for "Width" and "Height".
Click "Apply Width" and "Apply Height" to set the values.
Since you probably want to change a single value (width), simply change that one... unless you have various heights, of course.
You may have to re-align your string controls.
-JLV-