1 pound = 3500 calories, so in order to lose a pound a week, you have to eliminate or
use 3500 calories in a week. You can do that by cutting 500 calories/day, but that would make your caloric intake too little (never go below 1200 calories). You can also cut 250 calories/day from your diet and use up 250 calories/day in exercise. This is, by far, the best, and easiest, option.