You do not need to "uninstall" anything to switch to the nvidia binary driver, but you will need to edit the Driver
line in your xorg.conf file, changing "nv" to "nvidia" once you have installed the nvidia driver.
I don't use Scientific Linux, but if I rememeber right, that is based on RedHat is it not? If it is, then you should probably be using your package manager to locate and install the nvidia driver. If it is not, OR if you want to install the nvidia driver the 'usual' way, which is by downloading it from nvidia and running the built-in installer, then visit this page: http://www.nvidia.com/object/unix.html
and download a version of the driver that is appropriate for your hardware and operating system. There are good instructions on that page as to what you do to install the driver, but if you run into problems, just tell us what you've done so far, and what is going wrong.