Question

I would like on gridview update to get a value from a cell in the edited row for GridView1.Rows[get the edited row ].Cells[3];

Answer 1

You should handle the RowUpdating event:

 protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
 {    
    GridViewRow row = ((GridView)sender).Rows[e.RowIndex];
    String fourthCellstext = ((TextBox)(row.Cells[3].Controls[0])).Text;
    // .....
 }