You need to download the source and re-compile it. I personally create a shell script that I run for my PHP install, it looks something like this:
#!/usr/bin/bash
./configure \
--wiht-apxs=/usr/apache/bin/apxs \
...
I call this script do_conf, and I make it executable. Once I've got all my options in it and it works to compile PHP then I can just copy that script into my new source directory and run it, and I'll get the new version of PHP complied exactly like my old one. Remeber to use absolute paths, no relative paths, other wise you will have to modify your do_conf every time. And unless there is a compile option that gets changed in the new version you shouldn't have to modify do_conf until you decide to add more functionality.
