You'll be surprised of how little energy your body uses when exercising. I mean the other day I ran 2 miles on a treadmill and only burned off 400 calories, a snickers bar has 230.... so imagine the amount of exercise needed.
I guess you should start off with a healthy diet, control what goes in. Then exercise regularly, no need for it to be a bicycle, walking can do it. Just work up a sweat, just a little every day... and the improvements will soon come.
But don't expect immediate changes, it all takes time.