composer require magento/product-community-edition 2.2.6 --no-update
composer update
rm -rf var/di var/generation var/cache var/view_preprocessed generated/*
php bin/magento cache:clean
php bin/magento cache:flush
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento indexer:reindex
php bin/magento deploy:mode:set production
if you receive any errors post installation, try this hard fix
rm -rf app/code/Magento/ var/* vendor/*
chmod 777 -R *
composer update && composer install
php -f bin/magento setup:static-content:deploy
find . -type d -exec chmod 775 {}
find . -type f -exec chmod 660 {}
chmod u+x bin/magento
bin/magento maintenance:disable
bin/magento cache:clean
