In general, you search &download iOS ipsw from relational websites, and then use iTunes or iTools to restore your iOS device to the iOS firmware.
Now, you can skip the iOS ipsw searching, because 3uTools can automatically detect the iOS firmware compatible to your device and provides a very rapid
downloading speed.
http://tryimg.com/7/2016/02/01/HoXq.png1. Install &start 3uTools.
2. Connect your device to the computer via the USB Cable.
3. 3uTools can immediately show you which firmware versions are compatible to your device; furthermore, you can click the button “download” to get the
iOS firmware file you want.
*“Easy Flash” of 3uTools can help you restore your device to the particular iOS firmware with one click. And it supports iOS 4.0-9.2.1 flashing with
better user experience and faster speed.
*In addition, currently 3uTools can jailbreak iOS9-9.0.2, iOS8-8.4, iOS7-7.1.2, iOS6-6.15, iOS5-5.11 and iOS4-4.3.5 untethered.
http://tryimg.com/7/2016/02/01/HN1h.pngRegards,
if any help needed ask here ill try my best to guide.