|iOS 8.1.3 verifying update...|
When you want to update the software, I recommend that you check that you have enough storage space in the iPhone or iPad before performing the update. It is better to charge your devices to 100% battery life before the update. Do it when you don't need the phone or device for the next few hours just in case there are issues during update. I have been using iPhone, iPad for the last 5 years at least and I have never encountered issues during updating. Of course, don't interrupt the process of updating. Leave it there and the OTA system will update the device accordingly. That is why you need to charge it to 100% first before updating. Sometimes, I would leave it with the charger switched on just in case there was any issue.
Remember to backup your data before updating just in case. However, recently, I have not done any major backup and I have not encountered any issues. But like I said, just in case, you probably need to backup the device periodically so that you don't lose your important photos or files.