An FTP Server is built in in the SME server.
1. Go to the server-manager
2. Under "Security" click "Remote Access". -> Here you find "FTP user account access", set this to either "Public" or "Private" -> Scroll down and click the "Save"-button.
If you want FTP-access to an i-bay:
1. Create or modify an I-Bay (Collaboration->Information bays")
2. Set "Group"
3. Set "User access via file sharing or user ftp" to set permissions.