@Alain regarding installing:
You need to unlock the bootloader, there are plenty of how to's for that.
For that you will need a PC where the little tool fastboot is installed.
Then you might need to downgrade the device to the appropriate Android version. Usually the ubports installer gives short instructions where to download the right firmware.
After you unlocked the bootloader and the device is running the right Android version, you just use the ubports installer to flash Ubuntu Touch onto the device.
Thats it.