To make your shop a real beauty you should non-recurringly adjust image sizes for your products and re-generate all images using a plugin like Regenerate Thumbnails.
- Go to WooCommerce→Settings→Tab Products.
- Save the following image sizes:
- Catalog Images: 480 x 9999 pixels, Hard Crop: off.
- Single Product Image: 745 x 9999 pixels, Hard Crop: off.
- Product Thumbnails: 90 x 90 pixels, Hard Crop: on.
- Install the plugin Regenerate Thumbnails.
- Re-generate all images in your Media library.
- If you use a caching plugin like i.e. Cachify on your site, remember to empty your site’s cache.