How do I change the vibration intensity on my iPhone 4S on ios7

Try Settings > Sounds > [the particular pattern where you wish to change the vibration; e.g., Ringtone] > Vibration [at the very top] and change the vibration style there.

The following worked for me—the vibration intensity was greater independent of the Music app’s volume.

Turned off iOS 7's Sounds Setting for Ringer and Alerts>Change with Buttons, then moved the Ringer and Alerts sound level slider further to the right.

Hope this helps!