Hi Iom,
If you have not turned on Multi-Currency - You can do this by clicking on the Cog Wheel, Then Account and Settings, then Advanced, click on the currency section and you can change this using the home currency drop down box.
If you have turned on Multi-Currency, you are given a warning that you can't undo Multi-Currency, and you cannot change your home currency. If this is the case, you'll need to start with a fresh account.
Please let us know if this helps.
