Changing the Ringer Volume
Step 1 
Press the VOLUME key to hear a current ringer volume.
Step 2 While the ring plays, press the + or - on the VOLUME button to respectively increase or decrease the ringer volume to the desired level.
Changing the Handset, Speakerphone, and Headset Volume
Step 1 Increase the volume of your handset, headset, or speakerphone by pressing the + on the VOLUME button.
Step 2 Decrease the volume of your handset, headset, or speakerphone by pressing the - on the VOLUME button.
The VOLUME button adjusts the volume for the currently active voice receiver.