You can change the size of an image view component by creating new versions of the graphics to your requirements and then adding a new image set. (See the documentation for more details.)
You can change the default view size by creating a background image of the size that you want and uploading it. It can be completely white or transparent or whatever you need to force the size that you want. Images can be created with whatever graphics package you like, such as Photoshop, Paint.NET, or GIMP.