In order to withdraw, you will need to go to the 'My Account' section of the site.
You can find this in the top right corner of both the mobile and desktop site. Once you have opened the window, you can simply select 'Withdraw'
Alternatively, you can follow this link in order to place your withdrawal.
Once the withdrawal window is open, you will need to enter in the necessary details before clicking withdraw.
PLEASE NOTE: Your account will have to be fully FICA'd before your withdrawal will be processed.