How do I change the WooCommerce product page image dimensions?

Go to WooCommerce -> Settings -> Products and change the "Single Product Image" dimensions.

You will not see a change on product pages even though the images are being cropped to the sizes you specify because WooCommerce is still stretching the images to 48% of the container width. You'll need to edit the widths with CSS, e.g.

/* Image Width */

.woocommerce #content div.product div.images,.woocommerce div.product div.images,.woocommerce-page #content div.product div.images, .woocommerce-page div.product div.images {
width: 48%;
}


/* Container to the right width */

.woocommerce #content div.product div.summary,.woocommerce div.product div.summary,.woocommerce-page #content div.product div.summary, .woocommerce-page div.product div.summary {
width: 48%;
}