Slider picture too small

Hi,

I guess that you are refer to the Big Slide image, as I did not find any Revolution Slider on your homepage.
The image need to be at least 745x483 which represents the big image thumb size and the image needs to be of that width to fill the whole container. Regenerating thumbnails should solve it unless the image you use it’s smaller that the dimensions needed because WordPress doesn’t enlarge images.
If you use larger images please regenerate your thumbnail following this guide: https://forum.tagdiv.com/how-to-fix-strange-thumbnails/
Please try a plugin like Thumbnail Upscale to enlarge thumbnails: https://wordpress.org/plugins/thumbnail-upscale/ to enlarge thumbnail. For upscale use a combination of plugins Thumbnail Upscale + Force Regenerate.

Thanks!