How can I have rounded edges on my images with Wow Slider?

Ive tried every bloomin option but still can’t get Wow Slider to display my images with rounded edged like on this websites home page (They use Wow Slider as this is how I found out abotu Wow Slider)
http://formosamusic.co.uk/

Ive tried using gifs with rounded edged but that doesnt work either.
The above site are using JPGs though so I’m guessing its some setting in the options or some additional code?
Any help?

http://wordpress.org/plugins/wowslider/