Want to turn the ringer off unless receiving a transfer.

This feature determines how each outside line or pool assigned to an extension rings. You can specify Immediate Ring, Delayed Ring (telephone rings after a 20-second delay), or No Ring. Delayed Ring is useful for backup coverage on shared lines or pools, such as for secretaries who cover each other’s lines. No Ring is useful for all extensions except 10 when an operator answers all calls, or for telephones with no regular users, such as those in conference rooms. To change the way outside lines or pools ring at an extension:
To change the way outside lines or pools ring at an extension: 1 Press "Feature" , "00", "System Program ", "Central Tel Program" at extension 10 or 11.
2 Enter the number of the extension to be programmed for Line Ringing. The green lights next to the line or pool buttons show the current Line Ringing settings for all lines or pools assigned to the extension. (If a line or pool is not assigned to a button, the green light next to that button is off.) The following ringing options can be shown by the green light next to the line or pool button: • Immediate Ring — on steady • Delayed Ring — flashes slowly • No Ring — flutters quickly • Immediate Ring is the factory setting for lines; No Ring is the factory setting for pools.
3 Press the line or pool button until the button light shows the correct setting (the setting for the currently selected line or pool also appears on the display).
4 Continue programming, or exit programming mode.

Additional information that will be helpful. Although Ryancsmith's answer explained how to fix the problem, he left out two steps getting there. In order to get to "system program" you need to push the left intercom button twice. Then to get to "Central tel program" you need to push the right intercom button twice. THEN you can proceed with Ryan's instructions. I'm sure those things are second nature to him, but to us idiot out here, we need our hand held all the way through. Thanks, Ryan for fixing my issue.