Adjusting Image Sizes in Slider

When upgrading, the images in all of my existing sliders converted to thumbnails. I tried unchecking “show thumbs”, and increasing the main image width under the Slider tab in General Options but none of these changes affected the sizes of the sliders. I also attempted to create a brand new slider thinking this might make a difference, but it made no difference – old and new were all the same – just thumbnails.

Is there a way to fix this? I made the upgrade to increase the size of my sliders, and this made it even smaller which I found pretty comical.