If on 8.2.6.1 or 8.2.6, there's an easier upload path. Instead of launching an SFTP server, there's now the ability to create a transfer user so applications like WinSCP can work.
1) login to AMPCLI (with the configured 'ampadmin' acct)
2) 8 advanced
3) 7 add file transfer user
4) input desired transfer username
"When entering the username it must have 5 or more characters and contain only lowercase letters or numbers."
5) input desired password
"When entering the password you must follow these rules:
Minimum 8 chars with upper, lower, numeric, and non-alphanumeric characters. Spaces are not allowed."
6) connect with desired SCP/SFTP client
7) upload files into 'user' directory
NOTE: This transfer user will exist until the next maintenance cycle.
Then you can follow the menu item under security to apply the new SSL cert.