Flat sprints, hill sprints, jogging upstairs, biking and weight training are a good start. As for weight training I would start with squats bench press and dead lifts if your back is in good condition. You have to make sure your diet in in check though if you want your legs to lose fat. If your intake of calories is too high and your not exercising enough then you wont get the results you want.
walking up and down the stairs is really good! Did it for a long time during my break at work!
Walking up and down the stairs for however long you need uses a lot of muscles in your legs. Weight training, Step ups, aerobics.
An aerobics or gym instructor would be able to help you more with that :)