List box update in asp.net

Hi,

I have 2 list box left and right side. And one text box
Left list box data is coming from database.
First I m going to insert data so I ll write name in text box and select module name from left list box to right list box and save.

Now for updating I ll write name in text box and on text change I m writing code to get selected module name in right list box that also I m getting.

The problem is if I ll shift some module from selected list box to left list box for that particular name then how will I update this ....
If not clear plz tell.

Plz help thanks