Joomla! Documentation™

• First, review the system requirements for Joomla! 3.x and make sure that your server environment meets those requirements.
• Second, make sure that all your extensions (especially, your templates) are Joomla 3.x compatible.
• Third, create a test site and test the upgrade on the test site first.
• Fourth, consult a trusted developer if you’re not 100% certain about anything.
• Fifth, make a full backup of your site (files and database).

Once ready, go to the Joomla! Update component. Click on options and change the setting to Short Term Support. Save. You should be notified of the availability of Joomla! 3.x. Click the button to install. Clear your browser’s cache to make sure you see the latest changes. That’s it!

Finally, double check and make sure that everything is working properly.

See Planning for Mini-Migration - Joomla! 2.5 to 3.x and Joomla! 2.5 to 3.x Step by Step Migration for detailed instructions.

Note: On some hosts you may need to use alternative update methods such as using the extensions installer.