Changing bill to fields on sales order


i'm wokring on a task, where some modifications needs to be done. One of them is changing the bill to address fields. To explain it better, i also uploaded a picture below.

on a sales order, under shipping and bill fact box, there are 2 columns as you can see. ship to and bill to. When i choose alternative shipping address, on ship to, i want all the fields to be copied to bill to fields on right side so they are identical. for example, name, address etc. on left side should also be on right side. 

i tried some coding on the table, but it seems like the code does not work. Does somebody, have an idea how this can be done.

my guess to to add some code on ship -to code trigger, but i don't know where excatly.