Before you do anything please backup your Wordpress Database using a Wordpress backup plugin like BackupBuddy by iThemes.
1. To delete all your WooCommerce Products, for a fresh start, you will need to access the database directly via a database application such as phpMyAdmin (included in many hosting Control Panels). Navigate to your Wordpress Database and then in the SQL tab enter the following database query:
2. Click 'Go' in phpMyAdmin to run/execute the SQL Query. This will delete all your Woo Commerce products and their associations (including categories/taxonomies/terms info) so please exercise caution when running the Query.