How To change guiText's font dynamically in runtime(or) by script?

Try to create first the font materials you need your guiText's set to, and then use this bit of script:

 //Make sure this array is set with the fonts you need in the inspector!!
 public var fontMat : Material[];
 
 //This is where you set the default font
 function Start () {
     renderer.material = fontMat[0];
 }
 
 //To set default again
 function FontDefault () {
     renderer.material = fontMat[0];
 }
 
 //Use I.E: ChangeFont(2) to change to the second set font
 function ChangeFont (id : int) {
     renderer.material = fontMat[id];
 }
 //This is where you set the default font
 function Start () {
 
 }
 
 function ChangeFont () {
 
 }

Someone hopefully will know a more straight way of changing the font here, but the fonts always depend on font materials AFAIK.

It is in the docs actually:

Declare as many variables as you need, you might want to create an array. Then simply assign the appropriate one.

 var font1:Font;
 var font2:Font;
 
 guiText.font = font1;
 guiText.font = font2;