The Compact Disc shape has fixed dimensions and can’t be resized. The size is standard for Compact Discs, you need 12cm x 12cm images for front and back sides. As the shape is quite simple, there’s nothing to adjust in it, so no properties available.
Here’s how you can create a Compact Disc object:
var m = scene.root.addMesh("disc", "generator.DiscBox.Disc");