It is not possible to change the currency of your existing live account. However, you can add a new account in a different currency.
To add an account in the app, go to Home > tap the switch button at the top of the screen next to the account name > select the Live or Demo tab > tap Add Live account or Add Demo account > choose the account type and base currency.
To add an account on the desktop platform, go to Settings > My accounts > select the Live accounts or Demo accounts tab > click Add Live account or Add Demo account > choose the account type and base currency.