How do you change the voicemail message on the cell phone Sprint Nokia 6016i?

Whenever somebody calls me and I'm not there, the voice-mail message, or the part that says, "This is 'insert name', please leave a message after the beep, thank you", sounds like a ten year old version of me, because I forgot how to change the voicemail message. Please give me steps on how to change your voicemail message.