To update your voices, open the Infovox iVox Voice Manager and update your voices when prompted. You can also update your voices in the Infovox iVox Voice Manager by going to the top menu and selecting Infovox iVox Voice Manager > Check for Updates.... You should receive a dialog box alerting you that updates to your voices are available. Click the button for Install Update.
Note that you may also receive a message that you are running the latest version of Infovox iVox and no updates are available. Simply dismiss this message and your voice update should download.