On the mobile app go to the the Dashboard & scroll to your account balances. Tap on the Savings row to expand it
Tap on your Smart Savings account, which will be right below your bank account's savings accounts
Select Options in the upper right corner
Tap on Withdraw and enter the amount of money you'd like to withdraw from Smart Savings
Done! You should see your funds in your account within 1-2 business days.
Note: You can only make withdrawals on the mobile app & withdraw funds that have settled. Check the main page of your account to see if you have pending transactions.
If you want to close your account altogether follow this article here - How to: Close your Smart Savings account