For my theme Forest, I had to change the size of the WooCommerce Catalog Images, Single Product Image and Product Thumbnails. This can be arranged using the WooCommerce settings.
In my experience however, using the WooCommerce settings is not that user friendly, at least not if you are selling themes. There has got to be a better way! In this post, I offer an alternative solution.
Start by adding the following code to the functions.php of your theme. Even better: create a new file for all your WooCommerce code and include this in your functions.php.
You can use this snippet to set the size of all of the WooCommerce Catalog Images, Single Product Image and Product Thumbnails. Adjust the width and height to your own preference.
Curious how it turns out in your theme? Switch the theme off and on again. Your preferred sizes are visible at WooCommerce -> Settings ->Display.
When the theme is installed for the first time the preferred image sizes are already set. You can start uploading your product images right away. Alternatively, if you already have images in your image library, use the Regenerate Plugin to regenerate your thumbnails.
Great work, the above worked for me!