How many calories and how often i need to exercise to lose weight?

Try running on a treadmill instead of using a bike. You should burn more calories, running makes your whole body work out compared to just you legs with a bike. Doing intervals while running makes your body work harder, try running at a high speed for 1 minute and then slowing down for a minute, do that over and over. Also you can do upper body exercises, they help burn calories and you body will continue to burn them for up to 3 hours after you have worked out. Make sure you drink tonnes of water too, it helps burn fat. Check out menshealth.com they have lots of great workouts and tips.