Canonical has opted to enable by default the Nouveau drivers for Nvidia, in Ubuntu 13.04 (Raring Ringtaail). Unfortunately their drivers are not as good as the one developed by Nvidia.
I prefer working with commands so I will give you the way I had did it
Log out of the system and press Ctrl + Alt + F1. Log in into a command line , navigate to the folder where you have downloaded the driver, and kill the LightDM display manager:
sudo service lightdm stop
sudo chmod a+x NVIDIA-Linux-x86_64-313.30.run
All you have to do now is wait and follow the on-screen instructions. You might need to this operation twice if the Nouveau driver is active.
When the installation is done, enter the sudo reboot command and enjoy the newest Nvidia drivers.