How to update to Joomla 3 from Joomla 2.5
Joomla 2.5 is a long term release supported until the spring of 2014. All Joomla 3 version prior to 3.5 are short term releases which means that you shouldn't upgrade a live site from 2.5 to 3. You can do that after the release of 3.5. You can upgrade to Joomla 3 for testing purposes.
Here is how to do it with the built-in automatic updater:
- Back up the Joomla files that are on your Joomla hosting account and the database in which the application is installed.
- Check whether the third party extensions and templates that you have installed can be used with Joomla 3. If there are some that are not you should uninstall them, find similar extensions that perform the same functions, or reconsider upgrading your Joomla.
- Make sure that you use a newer version of Joomla 2.5 (e.g. 2.5.7) before you start the upgrade to Joomla 3.
- Log in to the admin panel of your Joomla and go to Components menu>Joomla Update and on the page that is displayed click on the Options button in the upper right corner. A new window will open; select Short Term Support from the Update server drop-down menu and click on the Save & Close button.
- The Joomla Update page will refresh and will display the newest stable update package. Click on the Install the update button and wait while the package is downloaded and your Joomla updated.
For some more details check out the Joomla 2.5 to 3.0 upgrade tutorial.