Reply To: Increase Height of Featured Image on Small Screen

@rawikltd : Go to Appearance => Customize => Additional css and add the following css.

@media screen and (max-width: 767px){
	#main-slider img {
		height: 300px;
	}
}

Note: The image may get elongated due to height restriction. Let me know if you need any further assistance.

Regards,
Tikaram