iOS8.1.3 will not update
The next solution to try might be to backup/restore your iPhone.

The Apple Store can help you with this, but probably not free of charge unless your iPhone is under warranty.

Fortunately, you can do it yourself, but you'll need to be able to log into iTunes with the same Apple ID that is used to identity you on the iPhone on a computer, and you'll need to be able to connect to that computer using a USB adapter cable.

If you can do that, then here's a pretty good description of the process:

http://www.uberphones.com/2011/05/restore-your-iphone-and-keep-homescreen-organized/.