When ever you change the theme, you might bump in to low resolution images being displayed for your category or product images. This is a common issue which was already noticed by WooCommerce developer. Therefore, they came in with a short video tutorial on how to deal with bad image quality in the category of your shop. Watch the tutorial below for more details:
https://www.youtube.com/watch?v=9wte-83NSnI&list=PLHdG8zvZd0E7s8CVjx3F89nsqGK7hrhbh&index=1