i'm disappointed to my HTML editing

Last fews days i was busy editing my blog template for originality but still i can't make right, the font of my post header is still messed up and i just dont know where to find the main body so i could change it. One more thing also is the color grey and yellow in this template supposed to float in the background color. I tried to edit it many times but nothing change the result still the same.Noticed that most of the font of my header are too way big, well i wanna change it to lil bit smaller or normal size but my question is HOW?and which one in my html should i go? I think i need help from you my co-bloggers and friends.I will really appreciate your help.

Thank you.