You need to update your personal information on Garmin Connect.
With your edge connected, at the top of the page select the Settings link.
Go through those and update all the personal information, weight, age. HR etc.
Then follow the instructions and let it update your Garmin 500 physical unit.
You will have to play around with the HR / Training zones as 5 zones are the least you can have. Know your resting and max and go from there.
Make these fit your known training/exercise zones and your calorie burn will be far more representative.