You might to upgrade an exitsing user to able to securely connect to server using SFTP (22) protocol instead of FTP (21). Before proeeding you might want to check if your current user has "ftp-user" privlidge or not.
In order to check that you can run the following command into the ubuntu server:
groups USER_NAME
If you see "ftp-user" in the output only then you should proceed further.
Moving...