If you want to update to i OS 10 smoothly, then this guide can help you: How to Prepare for i OS 10 Update.
If you meet some problems during the updating process, refer to this guide: i OS 10 Update Problems and Solutions.
If you haven't, read this guide to learn how to fix the problem of firmware file is not compatible.
Firmware file is not compatible that means the IPSW you got is not the right one for your i Phone, i Pad or i Pod touch, or your i Tunes doesn't recognize your firmware file.
Maybe your computer does not recognize the firmware file.