Sliders Pro Banner Resize

Hello all

I'm fairly new to web design.

The issue I'm having is when I upload my photos to 'Banners for Sliders' they are way to big. See image bellow.
This is twice the size, is there a way of changing it. I'm aware its probably something I'm doing wrong but I can't seem to find the setting to change it.

The images I'm adding to my banner are 1200x600 High quality JPG's.
I've also tried scaling them right down but the system just stretches the images and ruins the quality.

Is it possibly anything in magento that needs changing? 

If you could help I would be grateful.

Thanks 

Sion