Very easy. First do the driver steps above.
Then unplug everything from the current GPU (DVI/VGA cables in the back and PCI-E power connectors inside the case on the card). Then there is usually some sort of latch release you would press on the front (closest to the front of computer) of the PCI-E slot to release the GPU. Once you pull out the old GPU just slide in the new one into the same slot and plug the new cables back in. You may need to use 2 cables for the internal power connection, or an 8-pin connector instead of a 6 pin, depending on the config of your past and current GPU.
If you need a more visual explanation I would look on youtube. It's really easy.