It says fewer USD than blockchain.info for the same amount of bitcoins.
This is rather funny as Electrum uses the "blockchain.info" API for the exchange rates.
How do I update the exchange rate? Can Electrum automatically update the exchange rates?
When Electrum starts it fetches the latest data from "blockchain.info/ticker" and uses the 15 minutes average for the rates. If you need to update these quotes you've to restart Electrum.