Changed password on phone and forgot the new password. Phone is now disabled. How can we unlock phone?

Open iTunes on computer, connect iPhone to computer with USB cable. Hold both Home and Power buttons on iPhone until iTunes recognizes iPhone in Recovery Mode. This usually takes about 20 seconds of holding both buttons. Restore the iPhone Firmware. 

Or you can follow the steps in this article from the "erase your device using recovery mode" section at the bottom 

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support 

You wipe it and set it up as a new device.