On this page you will be able to download latest iOS firmware of iPhone 5s. You can use it for restoring your device into its original conditions. Flashing process will delete all data and content, including videos, songs, photos, contacts, and other information, and will restore all settings to their factory condition. Updating your device doesn't affect your content, settings or other information. In either case, backing-up your content in iTunes or iCloud is recommended. There are other flash tools and boxes which you can use as a flasher. You will need to always flash your phone with updated firmware. Flashing of phone does at those stage if pone is working slow or completely break with the reason of its corrupted firmware.