just to clarify that It's my first time I try to unlock and root my phone, so no much knowledge.
I basically followed the steps to unlock the bootloader.
Everything worked perfectly, I reached the recovery, went on 'apply update from ADB'.
But then, when I enter in cmd: 'adb sideload <whatever the filename>'
it prints out the Android Debug Bridge instructions rather than transferring the zip file to my phone, and the phone keeps on asking "now send the package you want to apply to the device with adb sideload filename "
N.B.: the phone is recognized by adb, even when I enter adb devices, it is recognized