Wow, I was searching for a similar question like this a few months ago. I google it and I found this link: answers.yahoo.com/question/index?qid=20090517102553AAwPQZK READ the 2nd comment. I got a some neck ache after I read this, I was laughing so hard...lol
First, you got to loose the weight - dieting.
Then exercise to tone it.- jogging.
If you run 2 miles a day for 1-2 months, you'll get the results. I've done it myself.
It's best if you do these at the same time for faster improvements.
You mostly want to do cardio. Burning fat means that you're burning fat all over. Fat gets stored a lot in the stomach but you have fat all over your body believe it or not. While you can do leg workouts, those will mainly tone the legs. I'd start off with a lot of cardio until you reach your ideal weight.
People think I'm crazy but Sketchers Shape Ups if you wear them religiously really work. I wore mine like 10 hours a day and was on my feet most of the time. Even gym rats were amazed at how much muscle I had in my legs and butt.
Do leg exercises, like walking, walking will help tone your legs out a bit, I walk 4 miles once a week in a trace at the gym (all at once) and I haven't seen a difference yet (because I recently just started doing it) but you will eventually start to tone your legs, also, try that rubber stretch thing where you lay on your back and you put this ribber sash thing on the bottom of your shoe and you hang on to either end one in each hand and you push your foot