Traditionally, Joomla website update had involved three methods: writing files directly, updating with a url for the file source and updating by uploading an update file. All of them are good and I cannot speak of any major advantage of one over the other except speed. Writing files directly can be faster than most other update methods.

There are cases when you are unable to use any of the methods, a manual update method will work in such cases and I will show you how to get this done in this post.

Why Update a Joomla Website?

Regular update for your Joomla website will help you keep your website operational in terms of security, usability and performance. This is a very important process that every business has to take into account to ensure that their website is still at its best.
The world of Content Management Systems (CMS) is constantly evolving, and users are very often not fully aware of the changes that apply to their own websites.

Credit: https://www.todhost.com/knowledgebase/806/How-to-manually-update-a-Joomla-website.html