Things to Do Before Installing iPhone 5s iOS 9.2.1
If you do decide to install the iPhone 5s iOS 9.2.1 update, you'll want to prepare. There's no way to predict what you might run into during the installation or after it so you'll want to make sure that you and your device are ready.
We've put together a game plan for you to follow. These are the steps that we take before we install an iOS update. It might seem like overkill for an update of this size but even the smallest iOS updates can cause problems.
At the very least, you'll want to make a backup of your files. You shouldn't anticipate losing any of your data/files but there's always a chance so it's better to be safe than sorry.