Updating product image

Propably you replace only original versions of images, but wordpress create a few this same images with different sizes.

After upload your photos you should regenerate thumbnails on wordpress dashboard.

You can use for it:
https://pl.wordpress.org/plugins/regenerate-thumbnails/

or little advanced: https://pl.wordpress.org/plugins/regenerate-thumbnails-advanced/

When you regenerated thumbnails, images should be correctly displayed.