I am lactating but I want to lose weight. Can I do that without harming my baby?

Eat well. When lactating you need can burn an additional 500cal/day just producing breast milk, which is great! you will continue losing weight as you breast feed (except for maybe the last 5-8lbs b/c the body needs the extra fat to help produce the milk). I recommend eating well with lots of fruits/veggies, lean protein, whole grains, and at least 8glasses of water per day to help make the milk.
Yes. You may want to enlist the aid of a clinical dietitian for guidance.If you consume a balanced nutrition based on your pre-pregnancy weight, supplemented with prenatal vitamins, you can drop weight and continue to produce milk.It is probably the best way to do it, and many fall into the trap of believing they must eat for two when breastfeeding.