1. Make sure you have the recommended Product Catalog image sizes set in WooCommerce Settings on the Catalog tab.
2. If you had existing content before activating CleanSale, or before setting image sizes in WooCommerce, you must run the Regenerate Thumbnails plugin, which you can search for and install under Plugins on the Add New tab. Please view the plugin Details before installing to understand what this does and how to use it.
3. If you want your main shop page product thumbnails to be larger than the related thumbnails, you will need to add the following custom css to override the plugin, and adjust the width as desired

.related img{max-width: 180px; height: auto;}