Before every update/upgrade, don't forget to backup your whole website and your database.
Extract the upgrade archive
Extract the update Zip archive using a file archiver software such 7-Zip.
Upload files to your server
Using an FTP client such FileZilla.
You must transfer ALL files and folders (even empty folders and files). Don't delete any files. just over write them.
If your OS server is a Unix-like, you must check if the file permissions (CHMOD) are correctly configured.
In numerical values that must be 755 for all folders and 644 for all files.
Warning, the following folders must have 777 permissions:
Warning, these permissions don't allow editing and creating files in the File Management admin module.
If you want to allow it, you need to set in numerical values 777 for all folders and 666 for all files.
Run the upgrade wizard
You must login as administrator and go to the following URL and follow the instructions carefully: http://YOUR-DOMAIN.COM/asset/file/Upgrade
Clear all caches through your admin panel.
Put back your modifications (optional)
Put them back any modifications you did from your latest backup since they could have been erase from the update.