How to access array position

1

i have an array and want to access the position of the array and replace by another number,how i wan do it.

var cardlist:Array = new Array();
for(var i:uint=0;i<16/2;i++) {
cardlist.push(i);
cardlist.push(i);
}

var mylist:Array = new Array();
var r:uint = Math.floor(Math.random()*cardlist.length);
trace(cardlist[r]);
trace(cardlist[3]);[COLOR=Navy]//how i wan to get position 3 data in the array
[/COLOR]