Hello i-Visio,
Thank you for getting in touch with us.
Please read about product images here – https://xstore.helpscoutdocs.com/article/89-product-images
It is recommended to use a graphics editor and prepare product images (make them the same size) before uploading images to your media gallery, or you can try to enable Crop via mentioned WooCommerce settings.
Also, it would be better to disable “Stretch product images option” option via Theme Options.
Best Regards,
8Theme’s Team