Unfortunately, the current version of Commander One does not allow to perform remote editing of files on FTP server. As of now to edit files properly you need to transfer them to your local drive, apply necessary changes and then upload files to a remote FTP server.
However, we would like to mention that the feature of remote editing will become available in the new build of the software. We are working on it now and we will certainly consider adding this useful option to Commander One.
As an option, we would recommend you to use CloudMounter software which was designed to mount cloud drives on your machine so that you could have access to them from the Finder.