the UpdateCommand affected  0  of the expected  1  records 

 Dim dt As New DataTable
    Dim da As OleDbDataAdapter
    Dim daTeachers As OleDbDataAdapter
    Dim dtTeachers As New DataTable
    Dim conn As New OleDbConnection

    Private Sub Form1_FormClosed(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed 
        Dim insCommand As OleDbCommand
        Dim upCommand As New OleDbCommand("update классы set класс=@par where класс=@par", conn)
        Dim delCommand As New OleDbCommand("delete from классы where класс=@par", conn)
        insCommand = New OleDbCommand("insert into классы (класс) values(@par) ", conn)
        insCommand.Parameters.Add("@par", OleDbType.VarChar,  15 , "класс")
        delCommand.Parameters.Add("@par", OleDbType.VarChar,  15 , "класс")
        upCommand.Parameters.Add("@par", OleDbType.VarChar,  15 , "класс")
        'upCommand.Parameters.Add("@par2", OleDbType.Integer, 4, "Key")
        da.InsertCommand = insCommand
        da.DeleteCommand = delCommand
        da.UpdateCommand = upCommand

        da.Update(dt)

End Sub