Here are the steps to install the GTX 550 Ti in your computer:
1. Power off your computer and disconnect all cables.
2. Open the computer case.
3. Locate the PCI Express slot on your motherboard. It is a long, thin slot with a metal cover.
4. Remove the metal cover from the PCI Express slot.
5. Insert the GTX 550 Ti into the PCI Express slot.
6. Secure the GTX 550 Ti to the case with a screw.
7. Connect the power cable from your power supply to the GTX 550 Ti.
8. Close the computer case.
9. Connect your monitor to the GTX 550 Ti using a DVI or HDMI cable.
10. Power on your computer.
11. Install the latest graphics drivers from NVIDIA's website.
Once you have installed the GTX 550 Ti and the latest graphics drivers, you should be able to use it as your primary graphics card.