My iphone 5 (7.1.2) won't upgrade to the newest update (8.1.3)?

My iphone 5 (7.1.2) won't upgrade to the newest update (8.1.3)?

Make sure that you have the space needed on your iPhone, and make sure that your iPhone is connected to Wi-Fi. If it doesn't work then, try restarting your phone? You might have to reset your iPhone to get the newest update.