Upgrade Magento 2.3.3 to 2.4

Question

How to upgrade Magento 2.3.3 to Magento 2.4?

Answer 1

First take to older version website backup and after your run direct magento 2.4.0 version.

Magento Open Source:

composer require magento/product-community-edition=2.4.0 --no-update

Magento Commerce:

composer require magento/product-enterprise-edition=2.4.0 --no-update

And you want to read more information check this :-

https://devdocs.magento.com/guides/v2.4/comp-mgr/cli/cli-upgrade.html

UPDATE:-

I will explain more in how to update latest magento version (2.4 at the moment):

composer require magento/product-community-edition=2.4.0 --no-update
composer update

If you are running Magento 2 commerce the command will be slightly different:

composer require magento/product-enterprise-edition=2.4.0 --no-update
composer update

Replace 2.4 with the latest M2 version.

When it is completed, run another SSH command and upgrade the Magento database:

php bin/magento setup:upgrade

After that you will want to recompile if you are in production mode:

php bin/magento deploy:mode:set production

You’ve successfully performed a Magento 2 upgrade! Now go to the frontend and backend and check everything.

THANKS.

Answer 2

In addition to above response which is fully correct, you can find this guide that I wrote and give all instructions plus a few more tricks: here

If you have MariaDB you will need to upgrade it, which is not straightforward but explained in that article. Also if you were not running with Elasticsearch as your default search engine you will need to install it and configure magento to do it.