Use following code to change different image sizes of woocommerce product.

• Change Product category thumbs
• Change Single product image
• Change Image gallery thumbs

Method:

1. Copy code to your functions.php.
2. Regenerate image thumbnails using plugins like Regenerate Thumbnails

/*
 * Hook in on activation
 *
 */
add_action( 'init', 'yourtheme_woocommerce_image_dimensions', 1 );

/**
 * Define image sizes
 */
function yourtheme_woocommerce_image_dimensions() {
   $catalog = array(
  'width'  => '400', // px
  'height' => '400', // px
  'crop'  => 1   // true
 );

 $single = array(
  'width'  => '600', // px
  'height' => '600', // px
  'crop'  => 1   // true
 );

 $thumbnail = array(
  'width'  => '120', // px
  'height' => '120', // px
  'crop'  => 0   // false
 );

 // Image sizes
 update_option( 'shop_catalog_image_size', $catalog );   // Product category thumbs
 update_option( 'shop_single_image_size', $single );   // Single product image
 update_option( 'shop_thumbnail_image_size', $thumbnail );  // Image gallery thumbs
}