Copy and pasted from the very excellent www.entropy.ch (Marc Liyanage).
Update Instructions
If you previously installed an older version of the module, here is what you have to do to update to the most recent version:
1. Open a terminal window
2. type "curl -O http://www2.entropy.ch/download/libphp4.so.gz", wait for download to finish
3. type "gunzip libphp4.so.gz"
4. type "sudo apxs -i -a -n php4 libphp4.so"
5. type "sudo apachectl graceful" to restart the webserver
The new version should now be active, you can test with the phpinfo() tip given above.