I'd recommned that you do some HIIT (high intensity interval training) 2-3 days a week and one LSR (long slow run) a week. A few different ways to do HIIT:
1. sprint 100 yards, slow jog for 2 minutes or the remainder of a 1/4 mile track, repeat 6-8 times.
2. Sprint up a steep hill for 100 yards, walk back down, repeat 6-8 times
3. run up a few flights of stairs or stadium steps (as far as you can go in around 30 seconds), walk back down, repeat 6-8 times
This is the best way to burn fat and increase heart-lung function and overall fitness with an investment of only 20 minutes time. Then once a week do a LSR of 20-40 minutes, as far as you can go and as fast as you can go and keep runnning the whole time.