I need to change the language in navigation system

You have purchased a Japanese Domestic model which most probably do not have an English version in it. If it has, you need to understand Japanese to be able to navigate through the menu.
The maps in the navigation is loaded via CD and meant for Japanese cities and unless you can get a compatible CD with your local maps, you cannot do anything about it.
You have the following choices.
1. Live with it.
2. Replace the navigation unit.
3. Find a whizz kid to reprogram for you, but this seldom works as some upgrading or modification needs to be made to the unit and it comes at a cost.