If you installed the theme on an existing site, you need to make sure the product image sizes in WooCommerce will fit your newly installed theme.
Where can I find the Image Size Settings for Products?
In your WordPress admin dashboard, navigate to Appearance > Customize > WooCommerce > Product Images.
There is no fixed size to be set for the product images, but you may want to increase or decrease the size. For example, if the images are looking blurry or pixelated, you'll need to increase the size to avoid having small images being stretched.