Changing of company currency in live environment

I want to change the company currency in a live environment in MSD AX2009. How should i go about it?Do we have to create a new company?Are there any Best Practices and Steps involved in doing the same?

transactions exist and this is the trading companies base currency?

Exactly.Transaction exists and this is the companies base currency

Then you need to create a new company. You can change the currency but no transactions will be revalued, which gives you a problem. Not sure there is anything you can do except create a new company.