FTP is the great way to manage your server's files with ease. It is useful for task such as uploading and downloading files such as worlds, plugins, mods, etc.
1. We highly recommend using an FTP client such as Filezilla, which you can download here. 2. Once you've got Filezilla, log into your Multicraft control panel and navigate to Files > FTP File Access. (http://i.imgur.com/AHHiUKN.png) 3. Copy and paste the "Host" and the "Username" from your Multicraft's "FTP File Access" page into your Filezilla client. The password is the same as your Multicraft password. 4. Press "Quickconnect" and you will be connected to your server's FTP so you can manage your files.
If you have any trouble with this, feel free to open a support ticket and we'll be glad to help you.