Volume control is one of the fundamental tools of the iPhone 4. Learning how to properly adjust the audio volume of your iPhone 4 will lets you decrease or increase the sound output of your speakers or earbuds quickly and efficiently. According to the iPhone 4 product information guide, "permanent hearing loss may occur if the receiver, earbuds, headphones, speakerphone, or earpieces" of the iPhone 4 are used at a high volume. Increase the volume of an iPhone 4 to a safe level to reduce the risk of hearing damage.
Locate the "Volume" control on the left side of your iPhone 4, beneath the "Ring/Silent" switch.
Press and hold the "+" volume control button to increase audio output; do the reverse with the "-" button to decrease the audio output..
Release the "+" or "-" volume control button when the audio output reaches a level you desire.
Drag the "Volume" slider of the on-screen controls in your iPod application when playing a song to increase or decrease audio output.