1. that depends on how you installed it.
- if you’re using WAMP or XAMPP, a reinstall of these programmes should suffice (note that they have to state in the description what PHP version they use).
- if you installed via php.net’s provided installer, uninstall it and install the new version.
- if you compiled from scratch, refresh the sources and recompile.
2. forgetting to save your previous php.ini settings
3. occasionally, default behaviour changes. e.g. register_globals is deprecated in PHP 5.3, XML handling changed radically from PHP 4 to PHP 5. nevertheless, all such changes are mentioned in the manual.
The computer is always right. The computer is always right. The computer is always right. Take it from someone who has programmed for over ten years: not once has the computational mechanism of the machine malfunctioned.
André Behrens, NY Times Software Developer