It is easy to do.
1. Download the ..zip package (NOT the .msi installer) from php.net/downloads
2. Extract the contents of the zip to C:/wamp/bin/php/php5.2.9
3. copy wampconfig.conf and phpForApache.ini from C:/wamp/bin/php/php5.2.8 to C:/wamp/bin/php/php5.2.9
4. Start WAMP OR right click the WAMP tray icon and select refresh from the menu.
5. Left click the WAMP tray icon and go to PHP > Version > 5.2.9
6. Go to [
localhost] version reported should be 5.2.9