Your best bet to convert Steem to fiat is to get on an exchange that trades Steem. Kraken does not currently trade Steem.
Some options are Bittrex, Binance, Poloniex or Bitshares.org. You can trade the Steem/BTC pair on each of these and some may have other trade pairs.
To get your Steem there, go to your wallet and withdraw Steem from your savings, entering the deposit address from your exchange (eg. Bittrex) account.
Hope this helps. Not sure of all of your fiat withdrawal options from these. I reside in Canada and find the easiest way to withdraw CDN $ is by transferring my crypto to Quadrigacx.
Thank you for those suggestions @cannonball6! Bittrex is currently closed to new registrations - and has been for months now. I have opened an account with Binance but I must get a "smartphone" for the same reason I need one for "e-pay" - in order to "confirm my phone" and get "authorization codes" in the various verification processes required by these entities.