SFTP Access on S5248-ON Switch

On my S5248-ON switch, I needing to use SFTP remotely using WinSCP to update the firmware; however, I get denied access when trying to access the switch.  SFTP is enabled on the switch.  The switch is new.  I have looked for documentation for the switch, but have not find anything about configuring access for SFTP.  What needs to be configured on the switch to allow access?  Thank you