مع العلم اني استخدمت كود 

 For i As Integer = 0 To Guna2DataGridView1.RowCount - 2

                Dim a As Integer = Guna2DataGridView1.Rows(i).Cells(3).Value

 Try
                    Dim cmdupdateitems As New OleDbCommand("update tbl_itembaseinfo set itemqty = itemqty +" & -a & " where itemid = @iditemtogetqty ", conitems)
                    cmdupdateitems.Parameters.Add("@iditemtogetqty", OleDbType.Integer).Value = Guna2DataGridView1.Rows(i).Cells(0).Value
                    conitems.Open()
                Catch ex As Exception
                    MsgBox(ex.Message + "خطأ   1")
                Finally
con.close()
                End Try