Check your current magento version

php bin/magento --version

Now Add the latest version to your composer.

composer require magento/product-community-edition 2.1.6 --no-update

Run Composer Update This will ask for the username and password take from your credentials from your marketplace account.

composer update

This will start process to start downloading and upgrading your magento

Finally Update you static content and remove var folder

rm -rf var/di var/generation
php bin/magento cache:flush
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento indexer:reindex

Recheck your magento version.