Simply go to your Accounts tab, click on your total balance to select the currency account you want to deactivate. Open the overflow window by clicking the three dots ‘...’ button and select “Deactivate”. You will no longer be able to send money using this account and linked cards, but you can still receive money into it. Your account can be activated again at any moment.
You can also remove the currency account only if there’s no money on it. Select your empty currency pocket, click the three dots ‘...’ button to open the overflow menu and select “Details”. Now open the overflow window by clicking the three dots menu and hit “Close”. All future transactions using that currency account will be declined and cancelled.