First go to http://www.nvidia.com/Download/index.aspx?lang=en-us and find the right driver for your gpu/video card and remember where you saved it then after it finishes downloading press Ctrl+Alt+F1 and put in your logins then cd to were you saved the .run file you downloaded then run the command "sudo service lightdm stop" and after that goes though run the .run file by this command "sudo sh ./file-name-here.run" replace file-name-here with the .runs file name and follow its instructions and after it finishes with the driver install run "sudo service lightdm start" and it should send you back to your desktop with your new driver up and running.