Feature image

I would like to upload an image, however when I upload an image it doesn’t encompass the whole width of the page where the call to action button is located. I would prefer not to have 3 headline sections and how can I remove the call to action button? If possible, how can I input a slider? Also, if I can input an image to encompass the entire area of the feature image location what will the dimensions of the image have to be?