To adjust the volume on your iPhone, access the "Sounds" menu in your phone. If you want to balance iPhone's sound you will need to go to the iPod menu.
Press the "Home" button on your iPhone and slide the arrow displayed on your iPhone's screen to unlock it.
Locate the application icon that says "Settings" displayed and tap it with your finger.
Locate the "Sounds" preference displayed in the Settings menu and tap on it with your finger. In the "Ring" section of the Sounds menu you will see a bar with a white circle, below where it says "Vibrate." Place your finger on the white circle and drag it to adjust the volume of your iPhone's sounds. Dragging the white circle to the right will make your iPhone's sounds louder. These sounds include your ringtone, new voicemail and new mail tone as well as your calendar alerts.
Press your iPhone's "Home button" and unlock it by dragging the arrow on the screen to the right.
Tap the "Settings" icon on your iPhone's screen and go to the "iPod" menu by scrolling down the Settings menu and tapping on the iPod icon.
Tap the option that says "Volume Limit" and you will be redirected to the Volume Limit screen. On this screen you will see a bar with a white circle. Place your finger on the white circle and drag it to balance the volume limit on your iPhone's iPod application. This will balance how loud or how low you want the audio to be on your phone. Once you have selected the volume limit, tap the bar that says "Lock Volume Limit" and you are done balancing the your phone's sound. After this task, when you listen to songs, podcasts, audiobooks, watch video podcasts or movies, your iPhone's sound will be balanced to your preferred sound setting.
If you are looking to balance the audio on your iPhone because you have noticed that sound is only coming out of the left speaker; do not worry, iPhone's only have one external speaker, the other is the microphone. Notice that when you listen to any type of audio with your headset, both sides will release sound.