Increase Size of Product Page Image Thumbnails?

When you upload an image, WooCommerce will make a thumbnail from it, in your case 250 x 250. This is the image that is sent from the server to the browser. However, when the image gets to the browser, the browser will resize it to fit the space allowed by the theme designer.

To change the size of the image as displayed, you will need to modify the theme styles. For help with this, in this case, please post the url to your site.