How to upgrade magento 2.X to 2.X?

Step 1: Access Your Server via SSH

You need to connect your server via SSH.

Step 2: Navigate to the Magento 2 Root Directory

Once your SSH connection is up, you will need to move to your target application folder. In that application folder, you will find the public_html folder which is the root directory of Magento 2.

Step 3: Upgrade Commands

composer require magento/product-community-edition 2.1.9 --no-update

composer update
rm -rf var/di var/generation
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy
php bin/magento cache:clean
php bin/magento cache:flush
php bin/magento indexer:reindex