Subversion is a version control system that makes it easy to get the latest version of files, or go back to previous versions. It is used by many different pieces of open source software and has been around since 2000. Subversion is considered the successor to the Concurrent Versions System.

Say you were running a Subversion server and your resume was checked into it when you first created it. Years later, if you have maintained your Subversion repository, you could go back and look at all of the changes you have ever made to your resume.

Subversion made upgrading a quick and simple event rather than a multi-day chore. Once set up correctly, there is very little you can do that will cause a mistake to be made. GeeksareSexy has written a nice article about ‘How To Upgrade WordPress Using Subversion‘.

First, upgrade your current blog using FTP, or whatever other method you choose to the latest stable version of WordPress.

Then, log in using SSH, and browse to your current blog. Go up one folder using the command cd .. in the terminal window.

Next, create a directory using mkdir. I usually make a directory called public_html_new.

mkdir public_html_new

Now browse into that directory, and using the instructions above, install the version latest stable version of WordPress using Subversion.

Once that is complete, copy your wp-config.php file from your old blog in the regular public_html folder to the public_html_new folder. This will allow your Subversion controlled blog to access your current blog’s database.

Next copy your wp-content folder from the old public_html folder to the public_html_new folder. This will give your new Subversion controlled blog all of your plugins, images, and themes.

Lastly, rename your public_html folder to public_html_old and then rename your public_html_new folder to just public_html. Check to see if your blog is working, and if so, you are most likely seeing your blog, now being version managed by Subversion.

Source: How To Upgrade WordPress Using Subversion