You can edit account from the My Accounts section that can be accessed from the Configuration menu or through the account details page accessed by clicking the account's name in the left side panel.
When editing an account, you can modify its name, its currency, its balance and the account type.
Chancing the balance triggers the account balance update procedure. For more details on balance update, read What does updating the balance imply?.
Changing the currency for the main account (named "Wallet" by default) will change the default currency for the entire account, and balances will be presented in the new currency.