updating video causes aspect change

I was working in iMovie 9 with videos created from old 8 mm films. I (probably foolishly) upgraded to the new version of the app, and when the old projects were "updated", the aspect ratio of the video was changed for a more modern screen, and the tops and bottoms of the scenes were all cut off. Does anyone know a way of undoing that aspect of the "update" short of going back to the events and trying to recreate the project?