Hi, hon --
Doing exercise and limiting your calories will help you lose weight in general. Cellulite is harder. (Are you sure it's cellulite? Orange-peel-type texture and cottage-cheese thighs like this?
http://www.cellulitetreatment.org/cottag… )
If you're already doing karate and walking and exercise, good on you! That means you just have to limit your calorie intake. Cut back on the fats that you use to prepare your veggies. Eat more whole grains and more vegetables. Don't eat veggie junk food like crisps, chips, or stuff like that.
You also might want to do exercises that focus on the specific part of your body you want to change.
Look out for "lose weight fast"-type pills -- a lot of them are scams! Be healthy and safe.
Good luck, hon -- be sure to come back and let us know what works for you!