Maps removal

Hi,
I have already got an excellent gift (Fenix 5x) from USA. As you know a few maps are included (USA, Pacyfic, Canada) which won't be used anymore. The question is how can I remove them from the devices. Europe map is bought and installed but I know that memory has a limited capacity. What is more Garmin Express notifies that all mentioned maps should be upgraded.
If you know how can I delete them I will be appreciated.