Can you please tell us, how you changed the currency? was it directly from the Database currencies table? if not...
You have two options.
1. Under admin -> System -> Settings -> Local (You can select the currency from the available list)
and if your countries currency is not there you can,
2. Under admin -> System -> Localization -> Currencies. (add currency of your country or that you require)
Note : When you add make sure the exchange value is set appropriately, and also the decimal.
Let me know how this works out for you..