Install fastboot package image

Make sure you have the latest platform-tools and Google USB Drivers installed (check #platform-tools).

Steps for installing a fastboot package:

1. Reboot to bootloader
2. Execute this for flashing the ROM:

A-Only
fastboot update
--skip-reboot aospa*.zip

A\B
fastboot update
--skip-secondary
--skip-reboot aospa*.zip

3. Reboot to Recovery.
4. Go to Wipe Data \ Factory Reset to format.
5. Reboot to System and Enjoy :D