Magento 2.1.18 is the final 2.1.x release. After June 2019, Magento 2.1.x will no longer receive security patches, quality fixes, or documentation updates.
To maintain your site's performance, security, and PCI compliance, upgrade to the latest version of Magento.

Prerequisites

Before running the Component Manager or System Upgrade, complete the following tasks:

Set up cron
Enter your authentication keys in the Admin
Set ulimit for the web server user
Checklist

After you’ve completed all prerequisites, continue with:

Start the Component Manager
Start System Upgrade

Sep 6th, 2018