If you've already built websites with Joomla 1.5 or Joomla 2.5, you can upgrade your existing site to the current version of Joomla 3.x. However, this isn't an automated process. How much effort this takes depends on what Joomla version your current site is running on and what extensions and templates you're using. So what can you do if you want to keep your existing content and the existing structure of your website when upgrading to Joomla 3.x? Here's an overview of the possibilities.
Tip
When you decide to upgrade your site, make sure you create a backup of your current site. This way, if anything goes wrong, you can always revert to the old situation. Akeeba Backup is a great (and free) tool to backup Joomla sites. It allows you to create a backup and also to reinstall that version of the site on a different location. This means you can copy the current site to a temporary location, perform the upgrade, and put the upgraded site back to the original...