All our servers support (i.e. are capable of running) both PHP 5.2 and PHP 5.3 (with a few exceptions listed below). The default version is 5.2.x but you can follow the directions below to use PHP 5.3.x instead.
Exceptions: Newer VPS/Plesk installations have PHP 5.3 as the default, and do not support PHP 5.2. Windows Shared & Chilisoft ASP servers only support PHP 5.2.
Before switching, be aware of backwards compatibility issues with scripts: Older PHP coding may not be compatible with newer versions of PHP.