The actual installation of a Graphics Card is very simple. Just insert it into your Motherboard's
PCI-E x16 slot (after having removed the Radeon from that slot), tighten the screws to bind it to the case and then connect the
PSU Power Connector(s) to the card. Job done.
Here's a guide with lots of info:
http://www.wikihow.com/Install-a-Graphics-Card
However, there might be some other issues for you to consider:
The
Nvidia GTX 650 really wants a
400w Power Supply Unit (PSU). Your current rig has a
350w PSU. The card may or may not run with such a setup. You can attempt to run it anyway with possible consequences being either your system won't start up with the card installed, or it will start up but the card won't function at full capacity.
Further, your system has a
PCI-E x16 1.0 slot. That's the slot on the motherboard you plug the card into. The
GeForce 650 GTX really want a
PCI-E x16 2.0 slot. Again, the card
will run in your current setup, though you'll see a performance loss of around 5%-10% due to your slot's comparatively low bandwidth to support the GPU.
Overall, your system should be able to support the card you've chosen, but bear in mind what I've mentioned in case you consider a PSU upgrade or a new system build, as the system you're plugging that card into is badly starting to show its age.