Each item of a list view is of
ListViewItem
type. A property of this type is SubItems, this is a collection of ListViewItems representing all the values for each column defined.
So in your case you want to change a specific column so give this a go:
ListViewItem myItem = listView1.Items[0];
myItem.SubItems[1].Text = "New Sub Item Value";
Ok in this case I have chosen a specific item, but you may want to use the SelectedItems property of ListView to retrieve your LstViewItem.
Hope this helps...