From time to time, as Magento improves its platform features, or to address bugs and security issues, you will receive a notice that your system needs to be upgraded. With Magento 2, this upgrade process is made infinitely easier and better than in Magento 1.x.
In order to keep your Magento installation upgraded, you must take certain steps:
In order for your store to communicate to Magento for upgrade verifications, you or a developer has to obtain developer keys. While this suggests that keys are only for developers, anyone can create an account at Magento and obtain keys.
If you don't already have an account at Magento, go to https://www.magentocommerce.com/magento-connect/customer/account/create/ and create your free account. Once you are registered, log in to your account at https://www.magentocommerce.com/magento-connect/customer/account/login/.
After you log in:


Now that you're able to communicate with Magento Connect, you can begin the process of upgrading your installation.
After entering your keys, you should still be within the Wizard. Find the System Upgrade button or sidebar menu and click it to begin the upgrade process.
The System Upgrade screen shows the steps the process will undertake to complete:

When this screen first loads, it goes through a series of checks to find out what needs to be upgraded. You can choose the version of Magento Core Components you wish to upgrade, as well as any other components that may have been added to your installation.
Once you make your choices, click on Next:

There are many reasons why an upgrade might fail. We have certainly had our share of issues, although far less with Magento 2 than with earlier versions. If you are a developer, you can find that most upgrade errors can be fixed by going to http://devdocs.magento.com/guides/v2.0/comp-mgr/trouble/cman/were-sorry.html and reviewing the advice shown there.
On the next screen, you can determine whether your installation is truly ready for a system upgrade. Click on Start Readiness Check and wait for it to complete its analysis:

Click Next to create a backup of your installation.
If you're not using a hosting company that provides backups or you do not have a backup protocol, well, you're flirting with trouble. No matter how well a server is configured or you maintain your Magento installation, you should never fail to make regular backups. As in this process, you should also make a backup whenever you make any changes to your Magento code.
In most cases, you will want to include all items in your backup. However, if your server is regularly backed up and you have lots of product images (for example, thousands of product SKUs), you might consider not backing up site "media." Media can take a long time to back-up and consume considerable space. However, if you update your media often, don't hesitate to include it in your backup.
Click on Create Backup to trigger the backup process.
When the backup is complete, click on Next. If all has gone well, the system will tell you it's ready for you to click on Upgrade.