Hello,
Find and replacee the code in your Theme Settings > Custom CSS
.product-label.new {
background-image: url(https://www.astemioconvertito.it/wp-content/uploads/2018/11/watermarks.png) !important;
background-color: transparent;
background-position: center;
background-size: contain;
background-repeat:no-repeat;
}
.single-product-content .product-images .labels-rounded .product-label {
min-width: 185px;
min-height: 185px;
margin-right: 0px;
}
You will get a result, like this http://prntscr.com/lj7nse
Do you still want to reduce the main product image?
Best Regards