how to update Magento via Copmoser

use SSH terminal, find public_html folder and type:

php bin/magento maintenance:enable
php bin/magento cache:disable
composer require magento/product-community-edition 2.4.3 --no-update (for version 2.4.3 -p1 use  "composer require-commerce magento/" but if you need install 2.4.3 -p1 you should install 2.4.3 first)
composer update
rm -rf var/di var/generation
php bin/magento cache:flush

sometime you need use this, but be careful:

php bin/magento cache:flush config
php bin/magento cache:flush layout
php bin/magento cache:flush block_html
php bin/magento cache:flush collections
php bin/magento cache:flush reflection
php bin/magento cache:flush db_ddl
php bin/magento cache:flush compiled_config
php bin/magento cache:flush eav
php bin/magento cache:flush customer_notification
php bin/magento cache:flush config_integration
php bin/magento cache:flush config_integration_api
php bin/magento cache:flush full_page
php bin/magento cache:flush config_webservice
php bin/magento cache:flush translate
php bin/magento cache:flush vertex

next step:

php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento indexer:reindex
php bin/magento maintenance:disable
php bin/magento cache:enable

After upgrade, check your Magento version with the following command:

php bin/magento --version