[Rabin Shrestha]

Hi,

The recommended image size for slider is 962px by 390px. You can have a look here https://www.themehorse.com/theme-instruction/clean-retina/#recommendedimagesize but the images currently you are using for your slide has image size of 564px by 390px try to upload bigger images of recommended size.

For changing the round image to square you can write your CSS in Custom CSS box in theme options panel.

Rabin