Itel it1556 official firmware requires Research Download Tool to flash. All required tool and relevant drivers are available in this post.
Download the firmware from the link below and follow flashing instructions after the download options.
File Name: IT1556-C195D-20160623.rar
Size: 597 MB
Firmware Link – Download
How to flash
Click here to download Research Download and Upgrade Tool, and learn how to use.