update Version problem

30-EVO-X

Any Ching can help me?

I follow other website try to update ipod touch 1 from 2.1.2 to Ver. 3.1.3
But in iTunes program it can't let me choose update what file
I downloaded 3.1.2 and 3.1.3 already, but update also can't choose file


Can any Ching help me plz