What you mean to say? In the above provided link, there is no any such slider. We are little bit confuse about your query, but as our understood, please add the featured image size of bigger image size. If you add the image size smaller, the size of image will full cropped and may be it losses the quality.
Or you mean to say that the image of the page you selected is not properly?
Please elaborate your issues with example too. It helps us to find the best way to solve your issues.