Corporate inertia

Hi
I have recently moved from many years of working for small organisations, to working for a very large japanese organisation.
I am finding that they not only have very different ways of working but also that they take an unduly long time to make decisions, which I feel can at times harm the business.
The management are largely untrained and very resistant to change, yet my manager hired me to start making changes.
What do you feel is the most effective way to instigate change in a large Japanese organisation ?

Regards

Carl.