How to Update WordPress site
You should always upgrade your site to the latest version of WordPress. Whenever there is a new WordPress version, you'll receive an update message on your admin screen. A site should be updated at the lowest peak time (at lowest traffic time) to avoid problems to your viewers.
There are two methods to update your site. One is with one-click update and other one is manually.
Backup your site
Before doing anything, backup your site for safe side. If there will be any issues you can restore your site.
Most of the sites automatically apply updates in the background. This is available for versions 3.7+
There are four types of automatic background update
In new versions you can update your site with one-click. This feature was added in the versions 2.7+. Whenever there is a new update you'll receive a notification. Just click on Dashboard > Update Screen option. You'll land on Update WordPress page. Now click on Update Now and the process will start. You don't have to do anything else. Once it is finished, you'll be updated.
When you receive a failed update message, delete file .maintenance, from your WordPress directory using FTP. It will remove failed update message.
If you are not receiving updates to automatic WordPress update in newer versions then you need to manually update your site. This could be due to many reasons.
Step 1:Replacing WordPress Files
In the last just have a look on wp-config-sample.php file to check for any new setting that need to be added to your wp-config.php file.
Step2: Update your Installation
Go to /wp-admin page. It may ask you to login again. If database upgradation would be necessary, it will give you a link to a URL. Follow the link and all the instructions, your database will be updated with the new WordPress.
Activate all the plugins in your site and start your work.
If you have cache enabled, clear the cache so that the changes will go live immediately. Otherwise, your visitors will see the old version of your site.