First off. See if you can get into recovery mode. Turn off phone and then hold the volume up, home, and power buttons at the same time. note this button combination may be different based on what phone you have. Look up your model. After you get into recovery mode see if you can restart your phone from there. If you still cannot restart your phone do these steps:
- Turn off phone
- Boot into recovery using the same method as before
- Select wipe cache partition - this will not delete any user files only temporary system files like those related to installations.
- Restart the phone
If that worked then there you go. You can try the software update again (make sure your phone is plugged into a charger so that battery loss is not an issue to interrupt your software update). If the phone still won't update post a reply so I can help you further. Hope this helped