How to lose weight quickly?

well i've been eating and drinking bad my entire life, and i want this to stop now, right now i am 5'10 and 192 lbs, and have some serious man boobage taking place, and my stomach is pretty big, and my torso is pretty much the only place i have fat for some reason :/ and i've started drinking only water and i used to knock back a gatorade, about 3-4 diet sodas a day, and my eating habits...wow, i used to have like nachos when i got home from school and stuff like that, but i have recently stopped snacking all together, so how much weight do you think i will drop by 30 days with that gone and also what exercise regimen should i get on and what should i pack for lunch each day, and i want to lose about 30-40 pounds by a month because that's when the dance is and i like this girl but she wouldn't go for a lard like me, so thank you and please halp me