This can be achieved by selecting the drop down arrow on the "Portfolio balance" section in the top left of the screen.

This will show a the list of supported currencies with a green tick (check mark) next to the currently selected currency.

Choose your currency by clicking on it. If you are in the wallets screen when changing currency, all the wallet balances will reload in the new currency.

If you are in a transaction list screen, you can force a refresh of the wallet balances simply by selecting the refresh icon in the top right as show below.