Main photo image far too big

Please post the url to a relevant page.

Thanks, Lorro, I should have done that initially.

https://www.ginneljewels.com/product/solid-short-sleeve-crisscross-tunic-plus-series-1-2-colours/

Whereas this one is much smaller. The originals are supposed to be 400px

https://www.ginneljewels.com/product/crochet-hem-detail-trapeze-tunic-sage-s-m-l/

.woocommerce div.product div.images img {
  float:none;
  height: 400px !important;
  width:auto !important;
  margin:auto;
}
.woocommerce div.product div.images .thumbnails img {
  height: 150px !important;
}

Custom css can be entered at:
Dashboard > Appearance > Customise > Additional CSS

You, sir, are a genius! Thank you very, very much.