Joomla org continously upgrades it's versions of Joomla, within a stream it is relatively easy to ensure a site is kept current and to improve it's security. As long as the core code of Joomla has not been modified then simply adding the latest files is all that is required.

However if upgrading between streams of Joomla is required  ( eg. 1.5.XX to 2.5 or 3.2) then:

are all required and the upgrade task can be quite complex. At NZJoomla we have considerable experience in upgrading Joomla sites and have undertaken many a site upgrade. These upgrades provide numerous benefits to your site:

Contact us now if you are interested in grading your Joomla web site.