Welcome to TTF.
On the unit, Manage Maps-->Switch map-->select the map you wish.
Be aware, if you do switch to, say, Europe_south, while still here in North America, in driving view, you'll see nothing at all since the gps signal can't place you in Europe at this time.
Nevertheless, you still can do Advance Planning on the Europe Map, add favourites and stuff like that. It's just the Navigate to functionality won't work while on this side of the pond.
Also, you HAVE made an Explorer, not Home, backup of your unit's contents, right?