D&D 3.5 Ed

Ok I play RPGs. I'm even such a nerd that I play them pen-and-paper. I play tested the one my brother is developing. Anyway long story short, when the 3rd Edition Dungeoons and Dragons books came out, I purchased them. Then a couple years later they came out with version 3.5... Crap now what do I do? What are the changes? This guy has some pdfs that explain.