When the theme is installed on a fresh copy of WordPress and WooCommerce it will set product image thumbnail sizes to be optimized for the theme. To confirm these have been set correctly, go to WooCommerce->Settings->Products Tab - 'Display' and scroll down to "Product Image Sizes". You should see the following.

If you see different image dimensions you should change them to match the dimensions above. If you've already been using WooCommerce with another theme it's likely that the thumbnail dimensions were different to that recommended for this theme. As a result, we recommend you use the Regenerate thumbnails plugin to regenerate thumbnails to be optimized for this theme.

Regenerate Thumbnails Go to Tools->Regen. Thumbnails and click "Regenerate All Thumbnails". If you have a lot of thumbnails this may take a few minutes to complete. Source image sizes We recommend you source images are at least 500px * 650px to ensure they appear correctly.