Want to remove the orderby dropdown for products?

To remove the drop down and ordering options completely, add the following to your functions.php file:

1	remove_action( 'woocommerce_before_shop_loop', 'woocommerce_catalog_ordering', 30 );

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However, if you want to edit the drop down and make it something else.  You can find the file at the following location:

/wp-content/plugins/woocommerce/template/loops/ordering.php

You can then copy that file to your theme folder, edit it, and override the default drop down.

/wp-content/themes/yourtheme/woocommerce/loops/ordering.php