I set up my outgoing message for when callers want to leave a message, but I want to change my outgoing message to them, and cannot remember how to do this.
Long press on the number 1 to access your voice mail and I believe you can also access other menu items at the prompts.
If you have Visual Voicemail, either start up the app in the app tray or press the Visual Voicemail icon at the lower left of the phone keypad and then press the "More" button on the upper right to access settings.