Featured images distorting

Hi,

I’m aware that this might be a theme issue but as I’ve had no response from the theme owners / creators hoping someone here can help me.

It seems that my featured images are being shrunk to 400 x 270 automatically (as shown when I open them in a new window) and then the home page is displaying them above the posts at a larger size of 489 x 330 making them distorted and horrible looking.

Can anyone suggest how I might fix this?

Thanks in advance.

The page I need help with: [log in to see the link]