Help with changing background music volume

[JackMonty]

I've created a menu screen which has a volume slider to increase and decrease the background music volume here is the script:

Code:

#--------------------------------------------------------------------------
  def update_se_regulation
    if Input.trigger?(Input::B)
      $game_system.se_play($data_system.cancel_se)
      @se_regulation = false
      @command_window.active = true
      return
    end
    if Input.trigger?(Input::C)
      $game_system.se_play($data_system.decision_se)
      @se_regulation = false
      @command_window.active = true
      return
    end
    if Input.repeat?(Input::RIGHT) and $game_system.se_volume < 100
      $game_system.se_play($data_system.cursor_se)
      $game_system.se_volume += 1
      @option_window.refresh
    end
    if Input.repeat?(Input::LEFT) and $game_system.se_volume > 0
      $game_system.se_play($data_system.cursor_se)
      $game_system.se_volume -= 1
      @option_window.refresh
    end
  end
  #--------------------------------------------------------------------------

The menu is supposed to allow the user to decrease or increase the background music - the problem is it only takes affect when the background music stops and starts again - not if it is currently playing, which is why I need to try and incorporate a stop and start value into this.