In DVDA double click on the first chapter (not in Preview). This will open the the whole show in the editing window.
On the upper right you find “Media Properities”.
Open “Track Media”.
You find “Video” and “Audio” When you click on these you find that you can delete and replace each track with a new MPG or AC3.
In the Editing Window below you can move the track markers to new positions.
JK