BMI will not be a big issue, however, don't take it lightly.
If you only reduce food intake, your body will get used to it and you won't reduce much weight.
Most important is physical workout.
Walking will get you nowhere in 6 weeks.
Jog as much as you can, twice a day if possible.
If jogging it is not possible, do leg exercises. Sit ups, or, squats with weight can replace jogging and reduce weight quickly.
Also drink at least two glasses of water BEFORE every time you eat, so that you don't eat too much.
I say this from experience, with all humility.