FTP is an insecure protocol that I suggest you avoid. If you must use it, though, be aware that it has a great many configuration options, which you can learn more about in Apple's documentation. Here, I cover only a few of the most basic parameters.
To activate FTP and adjust its settings, follow these steps:
Open Server Admin, which is located in /Applications/Server.
In the sidebar on the left, select your server.
If no services are listed under the server name, click the disclosure triangle next to the server name to reveal them.
If the service names are dimmed, choose Server Connect, type your username and password if they're not already filled in, and then click Connect. The list of services refreshes, and those currently running appear with a green dot next to them.
In the sidebar under your server name, select FTP. If FTP doesn't appear in the list, you must first add it by selecting your server name, clicking Settings, clicking Services, clicking the check box next to FTP, and then clicking Save.
If FTP isn't already running (that is, the dot next to FTP in the list isn't green), click the Start FTP button at the bottom of the window.
Click the Settings button on the toolbar.
Click the General tab, shown in Figure 29.4.
From the Authentication pop-up menu, choose one of the following:
Any Method. Uses either Kerberos or conventional cleartext authentication ...