Moving the first person controller upwards and downwards

Hello, I'm currently making a game where the player must avoid incoming projectiles, and during this development I've encounter a slight problem were I'm not sure on how to make the first person controller move either upwards and downwards (by default it moves forward and backwards).

Therefore I began searching through the first person controller script and encountered a particularly interesting function:

function Update () {

 // Get the input vector from kayboard or analog stick
 var directionVector = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));

I understand that this maps X and Z directions of the vector and puts 0 in Y. I was wondering if there was anyway way I could I swap the Y and Z to make it go up and down instead?

Thanks!