Hi there, so first
1. Slide to unlock your phone, if its locked
2. Then access the Phone app
3. On the lower tab, select Keypad
4. Press down on number "1" on the keypad until it says "Calling Voicemail"
5. If your voicemail is not setup, it will read instructions to you how to set up the voicemail
6. From the main menu you can customize, and update your voicemail settings