To edit the SN ID of a car, do the following:
Press the signal button
Click on "Deactivate unit"
When unit is deactivated, Click on the pencil to the right of the unit number
If unit is no longer connected to a car, click "Clear unit ID" to release the unit for install in another car.
If new unit is installed, click "Change unit ID" and click "Fetch unit ID" to automatically get the unit on this car. If this does not work, enter unit ID in the text field. Remember to click "Save" in both cases.
Check that GPS/GPRS say "Connected" in green letters. Otherwise the new unit is not installed correct or is defect.
Normally You should not click on "Activate unit" as the activation is done when connecting a Fleet or user.