I would change some of it. It wouldn't just be as simple as me changing who I was or how I thought, but also how my parents thought I should be raised. Quite complicated. If I could change those things, to change some of the past, I would. Not completely, because I am quite happy where I am in my life, but knowing the things I now know, and understanding so much better how life really works, and how other people really think, I could have easily done certain things differently back then to my benefit and ended up close to where I am now anyway.
A big one was woman. I had zero clue how to deal with them. Zero. I didn't get it at all. Just talking to them was enough to give me a heart attack. After my last couple relationships, my eyes were opened wide to the world of woman. Knowing what I know now, I would have had zero problems chatting up the ladies back then and actually getting somewhere. There are many things in life that are mostly smoke and mirrors at first glance.
I also would have bought an XBOX. When I eventually played Halo CE on PC, it blew me away and I never got to experience Halo 2 which sucked. My little bro hogged the PS2 a lot, so it would have been totally worth it.
"If only I knew then, what I know now".