i have that same problem!!

Stairs! the stairsteper changed my whole body..
that and lunges and squats.

Unfortunatly it is impossible to lose weight in just one place of your choosing (spot reducing) . A lot of people think that if they work one particular area they will burn the fat in that same area. This is a MYTH! Exercise and proper diet will help you lose fat overall but your body decides where it comes from first.

However you can concentrate on your legs when working out which will build muscle in that area and make it appear to be more toned but it wont spot reduce.

Hope this helps.