To backup your website, you have 2 options.
1- use a plugin such as BackUpWordPress. The installation and FAQ on the download page is pretty self explanatory.
2- to back up your website manually, you need to have access to your host’s panel, whether it’s cPanel or DirectAdmin, or …
Log into the panel, and find the database management section. Open it. You will see a list of databases in the left sidebar. Remember the name of your WordPress’s database. Now from the top navigation bar, choose Export and select the database that belongs to your website. If the database is huge, you can choose a compression method such as gz to reduce the download size.
Once you have backed up the database, head back to your panel. Find the file management and open it. Now choose the WordPress’s installation folder, and backup a folder names wp-content inside it. don’t forget to also backup the wp-config.php file inside the root folder.
If you want to be more secure, you can backup the entire root folder of your WordPress’s installation by selecting it, compressing it using file manager, and then downloading it.
Automatic update : After you backed up everything, you can simply use the admin panel of WordPress to update the core to latest version. You might also be asked to update the database too, which is an automatic process and won’t take long.
Manual update : To update your installation manually, remove the folders named wp-admin and wp-includes inside the root folder of WordPress, then download and extract a fresh copy of latest WordPress to your root folder, and overwrite every file. Now head over to admin panel and update the database. You are done.