You could consider using a PHP installer that would take care of upgrading Apache, PHP and everything for you automatically.
I use e-novative WAMP, available for free at http://www.e-novative.de/downloads. It automatically upgrades your HTML/PHP documents and databases, so you'll never have to worry about anything.
Why do it manually when there's an easier way to do it?
I found that manually upgrading PHP can be a problem when you mix up the DLLs. I once even crashed my system doing it.
Cheers,
Vanessa