How do I lose weight?

I have a gym subscription and I currently weigh 190. I walk on the treadmill fifteen minutes, do a stair stepper thingy for about five, lift fifteen pound weights (can't lift much yet, just started out) doing curls, side arm lifts, and I do twenty situps on an inclined plane. How long do you think it will take for me to lose weight and and how can I lose weight faster, without taking pills or some strenous diet?