I've been slowly losing weight over the past 10 months or so by doing about 1 hour - 1 1/2 hours at 21 mph on normal resistance. At first I wasn't sticking to my plan, which is to exercise every day for at least 40 minutes (at times I was skipping for weeks), but the past couple of months I committed myself to doing it for 5 days week minimum. I've had a couple lapses to my old laziness, but I've been fairly consistent.
That, combined with a healthier diet that I've been following (on and off like my exercise, but steady for past month) of whole grains, more fruits/veggies, no trans fats, low saturated fat, 1800 calories a day max, and green tea; stretching for about 20 minutes a day (my own combination of tai chi, yoga, and pilates); and light weight training and the occasioal sword/staff/punching bag training has allowed me to lose about 20 lbs (started at 195lbs, went down to 175). I've started to gain weight again, but it's almost all purely muscle since I actually look thinner, more muscular, and can do more strenous physical activities than I could before.
It's a lot better to make subtle changes in lifestyle that you can stick too rather than drastically changing everything. Just try and eat healthier, make a comprehensive exercise plan that fits your schedule. and you should be able to meet your goal. Looking at my fat ass body in the mirror was good motivation, along with reading health magazines (like Nutrition Action), which turned me off to unhealthy foods.
EDIT: Oh, and I'm 20, by the way. Here's another tip: make your own food when possible. Not knowing what's in your food can easily lead you to overeat. Planning meals is a great way to stay under budget. Knowing how many
calories you burn is another.