Picture Sizing Featured Slider

(I put it under this category because It would not allow me to select the current theme I am using)

My Featured Slider for my current Theme calls for a picture of 976 x 313. I re-size the picture while trying to maintain it without distortion. I can't get it to retain the actual shape of the photo. I'm sure there is a way to crop and still have a quality picture without editing so much of the photo, but I can't seem to get this right.