Before you update
When you receive updates, please do below steps first. These would help in preparation of the site and would avoid immediate and long terms stress.
You should have a staging server which is same as live server but it isn't live actually and is used to test out new versions of the software. Test updates on it without worrying about live servers.
Please read this document on how to create staging servers for Wordpress
You should backup your entire production server before you update our product. You can take a backup of your database and FTP your files to a backup location. There are many other convenient ways too to do this activity like use a backup plugin or a service.
Many free options available in our Wordpress.org