From time to time, you will eventually want to update your WordPress installation to the latest version from the official site. You may want to do it because you have seen a message on top of your dashboard telling you that an update is available, because you have been informed of new features that will be useful, or because a hotfix security has been published.
ATTENTION: The update process will affect all files and directories in the main WordPress installation. This includes all core files for operating WordPress, both extensions (Akismet and Hello Dolly) and the last default theme(s). If you have made changes to these files, your changes will be lost.
Check prerequisites system
Whatever the reason for the update, before beginning, it is best to check the pages of the prerequisites to ensure that your hosting has the required versions of PHP and MySQL. (If you are not sure, your web host will be able to tell you).
Make a backup
The next step is to make a backup of your database. All your articles and pages are stored in the database, so you will need to have a copy of it if for some reason you believe would change your mind after the update and that you have need to go back.
The last step of this preparation is to disable extensions. Well, it is not a mandatory step, but from time to time an extension has not been updated to work with the latest version of WordPress, and can cause problems. So it is best to try to avoid that, isn’t it?
You can easily disable all of your extensions by visiting the Plugins section in the dashboard and by choosing “Deactivate” option individually or check the boxes then select from the dropdown list “Deactivate” and then clicking on ” Apply.”
Ready to make the update!
Now that you have verified that your hosting is ready for the update, disabled your extensions and have your backup, it’s time to get started.
There are two methods of updating; The simplest is the auto update, which works for most people. If that does not work, or prefer to manage everything yourself, you can follow the manual update process.
Translated from WordPress.org