Making changes to the Flash Slide Size of images is easy but has some limitation.
The limitations are due to the fact that the images have to work with both the background main, text size relationship, and the fact that when you scale, the size changes include a change to the preview pane images at the bottom. There is always limitations with images that include text not being proportionally sized.
This is how we have found it best to make changes.
Take an original image for the module - that is 725 x 340
Use this size as a starting point in any other slides you produce. Then if you wish to resize a slide, still start with this original slide size in your graphics program, and either resize proportionally in that program or keep it 725 x 340 but ensure that you proportionally resize the module.
The module default size is 739 X 425. To work out a proportion simply devise one number by the other with a calculator.
eg 425 / 739 = 0.5751014 Then multiply this by your new width requirement
if you want a width of 600 x 0.5751014 = 345 for the height. New dimension for the flash slide module would be 345 / 600
This will five the best result for the resizing of images with text as a background.