Isotope Gallery Style

Good Morning,

I’m wanting to ask a simple question regarding Isotope with Oblivion.
I understand its not your plugin but all I want to know is how do I make the gallery look like the one you have on the theme preview?

On mine my thumbnails are displaying as the same size regardless of what size the image is.
On your the images are different sizes and shows as ‘staggered’

Hope you can help

Thanks
Paralysis