How can I change the data fields shown in the My Edge2 display ?

Very easy: you can use Garmin Express and search for applications and data fields installed on your device. Another way is through Connect Mobile. Android: you pair via bluetooth, after the connection is established, you touch the Edge 1030 icon and go to installed apps and data fields. There you can make the necessary changes or even uninstall. After everything is done, ask to synchronize. Done.

Thanks you George, but I can' t "delete" for example the indication 'power' and replace it by 'altitude' or 'heart rate' or another  indication...

You cannot "delete" the field. You can leave it blank by choosing "none" or "blank". However you can substitute for all the options available in the list.