How do I exchange large amounts of money internationally?

I have recently been working in the UK and have saved a bit of money. I am now moving back to Australia and I need to exchange and transfer the money from pounds into dollars into my Australian account. Do I do this before I leave England or do I do this when I arrive in Australia?

Also will I be charged for this and if so is it a percentage or a fixed fee?

Also should I do this on a day when the pound is high and the AUS dollar low?How do I exchange large amounts of money internationally?Use half of your money to buy a draft in Australian dollars with a London Bank.Take your remaining money in pounds back home. When you exchange your pounds, exchange when its rate is high against the AUS dollar.This way you get more AUS dollars.