Uninstall?

Three weeks ago I was working through the Lynda.com "PHP with MySQL 
Training" because I wanted to begin using PHP (surprise, surprise).

Anyway, on this video course the teacher explains that because installing 
PHP and MySQL is so well understood on a Mac that we may as well just follow 
his steps and do it manually.  Well, he is installing a different version of 
PHP and MySQL to the ones that I was able to download and while what he was 
saying way somewhat similar I am guessing that  there is a difference 
somewhere, and (well) it's not working.

I AM A COMPLETE NOVICE WITH LINUX/FREEBSD.  It had not been my intention to 
learn the intricacies of Linux.  However, I am now neck deep in a mire of 
confusion that even MAMP can't seem to sort out for me.

It is purely a guess that I need to start again from a complete clean setup 
(reformatting my hard disk and reinstall OS X again) but that is pretty much 
out of the question.

I guess my question is:

"How can I completely uninstall PHP so that I can start again?"

Thanks.