Need to lose over 80 lbs

Well, for starters I'm trying to lose a lot of weight. Ever since I went away to college, I've been eating really bad, not working out, and I've gained over 30 lbs. I was about 160-170 when I started school...now I'm like 200 something lbs 
I haven't had the motivation to work out either. I tell myself that I'm going to get up and workout but never do and while I'm at school, I can't seem to make time to workout.
How can shrink down to 140 while I'm at school and how can I have the motivation to eat right and workout?