Before any changes in your current installation you must make copies of the database and the roor folder of drupal. 

Step 1

Download the latest version in .zip or .tar.gz format from drupal.org/download

Step 2

In the root of your installation remove the folders core, vendor and all the files in the root directory except gulpfile.js and package.json (remove hidden files too)

Step 3

Extract the compressed file from the new downloaded version in the root folder of the installation. Be aware of the hidden files that you have to extract too.

Step 4

In your website (while logged in as admin) run /upgrade.php. This will update database schema and make all the changes.

 

Lastly, check in administration of your website on /admin/modules and admin/modules/updates to confirm the new version of the core and the modules.