If you can, use a stair climber, if you don't have access to one, try using actual stairs. Leg lifts, leg lifts using weights even better, squats are awesome and you are already doing those. Keep up with your cardio(the running) avoid fatty, sugary foods... try to eat the right amount of calories and good healthy nutricious foods to make the most of those calories. Can't tell you how many you should be doing, but if you youtube up some squatting videos you can check out and make sure your technique is correct firstly before exhurting yourself to something not so effective.
You should be doing them daily, amount can increase as you go along. Its best to do them in sets then break in between... but how many reps and how many sets are dependent on your fitness level, etc.