In Slide Opions, look at the bottom of the screen. Notice the magnifying glass icon. It is set at 100% zoom by default. If you change that to say 20%, you'll be able to see the entire slide.
BUT !!!!!
This is a rather complex style, and changes must be made carefully.
The style uses 15 images and 15 duplicates of these same images, and they all slide to the left.
Moreover, this style is based on precise calculations.
Notice that image 1 is placed at the values of x=0 and y= -33.33. These are the values of the topmost middle image.
All the remaining images are placed in relation to this first image, at a distance of either +33.33 and -33.33, or multiples of these values.
So any change that you might do must take into consideration these values.
For short, it's not so simple as you described it.
In any case, if you do change things, just by dragging things around a bit, without any calculations, don't forget to make the same change in both keyframe 1 AND keyframe 2.
Also notice that this style uses modifiers to make the movement to the left. So, whatever you do, don't touch the red dot that you see next to the values of x and y, and don't play with the zoom values.