Have you done an RPM install or installed from source? It shouldnt be too hard to upgrade. If RPMs you should be able to find one freshrpms.net or rpmseek.net
If you built from source go into the build directory copy the config.nice copy it into the php5 directory for installation. If your using mysql make sure you edit it to allow MySQL to install
--with-mysql=/path/to/mysql
If you have extensions to add now is the time. Then making sure config.nice has executable permissions chmod a+x config.nice and run
./config.nice
make && make install
You will probably need to copy the php.ini-dist or php.ini-recommended to the /path/to/php/lib as php.ini then if your using Apache make sure your loading the php5_module instead of the php4_module and restart your server.
If you havent got a phpinfo now is the time to create one and check that php 5 is working.
