I downloaded NVIDIA-Linux-x86-295.59.run from the official Nvidia website, I used in the terminal sudo sh NVIDIA-Linux-x86-295.59.run the installation started and everything, but I got this ERROR: You appear to be running an X server; please exit X before installing. For further details, please see the section INSTALLING THE NVIDIA DRIVER in the README available on the Linux driver download page at www.nvidia.com. I'm a newbie to ubuntu, and I don't know so much codes, can you please tell me step by step?