Ajax Nav
From version 5.2 onwards, inbuilt support for AJAX nav has been discountinued. Due to loading issues and only 5% users ever needing it. If you would like to have a rich user experience with AJAX navigations on SHOP pages, you can download and install https://wordpress.org/plugins/yith-woocommerce-ajax-navigation/ plugin. This plugin heavily integrates with the theme.
After activating the plugin you can follow this extensive documentation http://yithemes.com/docs-plugins/yith-woocommerce-ajax-navigation/ to setup the ajax navigations.
Note : If you are already using ajax nav from old versions of the theme, nothing to worry, they will continue to work if you activate above plugin.
Further recommended reading (official links):
- Product Attributes http://docs.woothemes.com/document/managing-product-taxonomies/#section-3
- Product Variations http://docs.woothemes.com/document/product-variations/