Your body will need more calories, not less. That it needs less is a misunderstanding of your needs.
Absolutely your body requires less calories the less it weighs ... to MAINTAIN the existing weight. You are losing weight, and chances are you're doing that by creating a deficit that is as large as safely possible (because we all want to lose as quick as we really can).
Say, for example, you're aiming for a pound a week now. As you lose weight you'll find that harder to achieve and the closer you get to goal weight the more you need to eat for a half a pound a week - by eating 250 more calories.
A 250lb person needs around 2300 calories per day and can create a daily deficit of 2lb/week (1000) so eat 1300 calories.
At 180lbs, she may only be losing a pound a week now, a daily deficit of 500. Her body needs 1900 now (less, see? It works here), so she eats 1400 (more, see?).
At 150lbs she needs 1750 a day (less, again) but may lose at half a pound a week (250 daily) so eat at 1500 (more, again).
At 125 pounds she now wants to maintain. Her body needs only 1600 calories (less, again), so she eats 1600 calories (more, again).
So while your body requires less calories to maintain the less it weighs, generally when dieting your amount to eat will increase until you are maintaining your ideal weight on a lot less calories per day than your original weight required.
Anyway, as Becky said, this'll be calculated for you any time you save the Weight Goals page or the Fitness Goals page. Those pages are used to calculate your range. Just make sure your expected rate of loss is appropriate for how much you want to lose (you can't lose 2lb/week for 20 weeks and then instantly maintain on the 21st week - you need to slow it down as you get there).
Deb, in New Zealand