I've just tried to increase the size of your competition entries, but unfortunately the resolution of the images makes them too grainy when I make them bigger. For instance, if I make this one bigger:
...the quality of the image is lost. Have you still got the original image files, and do they look OK on your screen?
Just for info, to increase the size of an image, you need to put a Width tag in, so where you see the [IMG] piece of code, you need to add in the width size, so it should look like this: [IMG width=800]. A width of 1000 will fill the screen, 500 is half the screen, etc.