Due to complicated nature of Joomla CMS upgrade to latest version can be quite difficult and scary exercise. Sometimes, it is even better to wait longer for LTS ( long term support).
First questions is always:
Do I need to Upgrade Joomla 2.5 Now?
In most cases the answer would be - NO! For instance Joomla 3.3.0 is still unstable release and many components and templates might show errors or incompatibility. On the other hand benefits might look a lot at first, but in reality 2.5 is quite capable and modern.
The answer for Joomla upgrade would be YES, if you are building brand new project, you want to be early adopter and you want to stay in-tune with latest technology.
How to Upgrade Joomla 2.5 to Joomla 3.3?
There isn't a definitive answer of this question either. It very much depends on the whole setup. As I mentioned before, Joomla have complicated structure itself, so the right course of action depends on number of extensions, templates, plug-ins and custom code (if any).
I will try to clarify the right steps for migration, which will reduce possibility for error dramatically.
Before You Update Joomla
I will share, what I did at during WebmaisterPro upgrade. Some steps are optional, but I would say that it is better to be on the safe side and follow everything strictly.
Back-up, Component and Templates Version Check
The first thing to do is to create backup. I personally prefer creating backups with Akeeba Backup. Keep in mind that untested backup is not such a good idea. Make sure that your backup works. As well as make a backup with your cPanel.
Check and upgrade all extensions to latest stable version
Create a list of all components (easiest way is to put everything on paper). Visit extension developer website and verify, if the extension is compatible with Joomla 3.x.
If an extension isn't compatible or require different version to work with Joomla 3.x, unistall this extensions, the same thing apply for templates. Many templates have different version for Joomla 3
Check Your Server
Joomla 3.3 require PHP 5.3.10+, though I think that it is more than adequate to use PHP 5.4+, as 5.3 is already discontinued. You also need to make sure that PHP Magic Quotes GPC is off. For additional information about system requirements please visit this link:
To be on the safe side in addition to your backup, would be a great idea to create SQL dumps on all different components and contents.
One-Click Update Joomla 2.5.20 to Joomla 3.3.0
Since Joomla v 2.5, there is so called “Joomla Update” component that appear under components. If you aren't familiar with it and if you are already using Joomla 2.5.20, you will see “nothing there” as default setting is set to LTS releases. Click options and check “short term support”, then you will be able to see latest version.
There is just one step left, to click install.
In general upgrade isn't very difficult and if you follow the above steps, everything should go smooth. Of course there might be minor hickups with templates or components, but these would be easy to tweak.
Have you already upgrade to Joomla 3.x? Please do not hesitate to ask me any question, regarding migration process or benefits of Joomla 3.x vs Joomla 2.5.x!