Make sure you have installed and activated both Real Estate Manager and Currency Switcher plugins. Now navigate to the Real Estate Manager -> Currency Switcher and configure the settings.
You have to choose a live exchange rates provider. Google and Yahoo are free, for others, you will need to provide an API key.
This option let you control auto-fetching exchange rates by registering cron jobs.
Switcher in Menu
You can enable or disable the switcher in the menu.