How to lose a very fat belly?

I am 5'7" male, 27yrs and weight 85 kgs and I have got a very fat belly. I use to walk for about 4 KM everyday and lost some weight too; but I was unable to continue walking due to lack of time for the last 2 months and have put on a lot of weight. what are the ways in which I can reduce my fat belly and bring my weight to normal ?