You will need to uninstall PHP and then reinstall the older version. However, if you are working on a project that you intend to sell or provide to customers, or whatever the case, my suggestion would be to pull out any functionality that actually breaks between 5.2x and 5.3x and replaces it with new counters, since most people they don’t want to go back to older versions of PHP for any needs, and, generally speaking, php versions will go in only one direction if you lock yourself in 5.2 and make software in one form or another for people that you are going to de next year, when all the servers will come with PHP 6? Not to mention the fact that many hosted solutions try to provide the latest and greatest new machines and will not return for one client,especially in a co-location environment.
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