how to fix iphone 5s that locked up after ios 9 install

Hi. Please specify what do you mean by "locked up"? Describe the issue in more details.

If it is stuck on slide to upgrade screen: If your iOS 9 device is stuck on Slide to Upgrade - Apple Support

Try to reset your device. This won't delete your data stored on this device.

• Press and hold the Sleep/Wake button
• Press and hold on the Home button
• Keep holding both buttons until the display turns off and back on with Apple logo on it.