Hi.,
We create the test IMAGE CAROUSEL item Please refer : http://zentre.webapunt.com/qui-som/
Get into Admin Panel > Appearance > Customize > Additional CSS > Paste the below css code inside the text area > Save All.
.dt-sc-images-carousel li img { height: 512px !important; width: 512px !important;}
Note: You can change the height and width value as per your need.