There are three ways to lose fat:
1) Have it physically removed (liposuction)--not a good option. You will have the same amount of fat cells for your life. There is no losing fat cells, though you can clear the cells of the fat, so they lay flat. People who are genetically heavier tend to be born with more fat cells, so even when they are cleaned out, there are more empty cells.
2) Clear out fat cells using diet (creating calorie deficit). By eating less calories and healthier food, along with exercise (which burns calories), you will lose weight because your body will burn fat when it doesn't have calories left (provided you fuel your body enough so it doesn't go into 'starvation' mode. A good start is slowly trimming down 100 calories a week, until you've cut about 400 calories for each day--along with exercise, you'll lose over a pound per week).
3) Burn stored fat in your workout. When your body works, for the first 20 minutes or so, your body is burning glucose, or sugar, in your body. It does not burn stored fat. After 20 minutes, you will start burning fat, depending on your heart rate. At very high heart rates, you're burning more of the food you've eaten and less stored fat. With HIIT, you will hit this fat-burning cycle faster than steady-state cardio. But it's also harder. You should have a variety of cardio exercises that keep your body guessing to burn maximum fat.
So the point is that if you're running for 20 minutes, you are still burning calories which will create a calorie deficit and you will burn fat that way. If you run longer than 20 at a moderate heart-rate, you will peel off both fat and calories. At what is considered your AT (or anaerobic threshold), you will be burning maximum fat and calories.
It seems like you need to increase your time, so I'd include one HIIT day, one day of longer, low-intensity cardio (maybe an hour of walking at an incline, for example), and one day of steady-state cardio.
I personally find that the best way to burn fat is to include these and any additional days you can do more steady-state cardio, though this should be a different exercise than you've done the other three days. When you're burning fat instead of calories constantly, you get less tired and don't get light-headed, because your blood sugar is not plummeting.
Good luck!