Here is the detailed step to step guide that will help you do so
Register yourself at https://www.poloniex.com
Once logged in go to this link https://poloniex.com/balances#SBD
You will see these options as below
Copy your Steem Dollars MEMO and Poloniex’s Steem Dollars deposit address
Go to your Steemit Wallet
Click down arrow in Steem Dollars and select Transfers
Fill in the details like Poloniex’s Steem Dollars deposit address, Steem Dollars MEMO which we got earlier and amount of dollars you want to withdraw
Click Transfer
Now wait for 10 minutes and you will see your money transferred to your Poloniex account here on this link https://poloniex.com/depositHistory
Next Step how to convert SBD to Bitcoins
Go to this link https://poloniex.com/exchange#btc_sbd
Click You Have and Highest Bid under Sell SBD as shown in the image below
Click Sell that’s it now you have converted SBD to Bitcoins.
Now we need to convert Bitcoins to USD/Euro or your countries currency.
To do that we will use Payza you can sign up for payza here http://bit.ly/2axArTJ
Once you Login to your Payza account click Add Funds Option and select Bitcoin
Enter the Bitcoin amount you want to withdraw (The amount you have in your poloniex account)
On this page you will get your unique Bitcoin Address copy it
Now we will go to our Poloniex account using this link https://poloniex.com/balances#BTC
Click Withdraw and paste in your Bitcoin address and amount you want to withdraw.
That’s it within 10 minutes you will see your money converted to your currency and deposited in your Payza account.
From there you can withdraw to your bank account using this link https://secure.payza.com/WithdrawFunds.aspx
I hope this will help you withdraw your money to your bank account, If you are having any issues you can ask me in the reply section.