I feel this is an awfully obtuse question to ask, but strangely, this problem is poorly documented.
I would like to upgrade PHP, but there are several problems:
You can use curl to update php version.
curl -s http://php-osx.liip.ch/install.sh | bash -s 7.3
Last Step:
export PATH=/usr/local/php5/bin:$PATH
Check the upgraded version
php -v