PrestaShop 1.6.x. How to change default filtering option on products page

1. In your PrestaShop admin panel go to Preferences -> Products section: 
2.  Find Pagination section there: 
3. In the Default order by field, you can set the default product ordering by name, price, date etc. Choose the filtering option you want to be the default and click Save button in the right bottom: 
4. Refresh your website. The default filtering option has changed on the products pages.

Hopefully, this tutorial was helpful for you.