How to update/fix WooCommerce out of date?
Fix out of date, have 2 solutions:
1. Do follow guide from author of WooCommerce here: https://docs.woothemes.com/document/woocommerce-self-service-guide/
2. Do follow:
2.1 Go to list file had warning,
2.2 Scoll down to Templates, then find exactly find had warning on your hosting/server, example here
In image, path is [themename]/woocommerce/product-searchform.php
Open/edit it, then edit/change value below to latest version as you want: