Thank you for the suggestions. I actually do have Illustrator but pretty new to using it. I was at last able to upload to NivoSlider a png file that have the dimensions 1000 x 521. However, the slider is showing nothing on the website after updating multiple times. I also tried uploading two images with the exact same dimensions and settings, but getting the same empty space with no images.
Out of all the themes I’ve tried as a novice, StartupWP by far has been the easiest to use for most everything else. I would truly appreciate any help!