Step by step:
Here you go:
1. Before you buy a graphics card, make sure that your machine's power supply is up to the task. Check the manufacturer's specs for minimum power requirements before you take the plunge.
2. Ensure that the case has enough room for the new card. Graphics boards have become longer over the years, and the space in older cases may be a little tight.
3. Download the latest driver for the new graphics card. Don't install it yet.
4. Uninstall the older graphics drivers. Even if you're installing a GPU of the same brand as before, removing the older drivers prior to installing the new card is a good idea.
5. Power down the system.
Carefully disconnect the power cables from the old card and remove the screws holding it in place.
6. Remove any power connectors from the old graphics card. Also remove the screws that attach the connector bracket to the case.
7. Ensure that no clutter--cables or wiring--surrounds the card. In addition, large CPU heat sinks can interfere with physical card removal or installation, so you may need to remove the heat sink. Be sure to detach the monitor cable from the old graphics card's outside connector, too.
You might need to hold a latch down with one hand while removing the old graphics card with the other.
8. Most motherboards have a little latch that locks the graphics card securely into its slot. You may find it necessary to hold this latch down (or aside) while removing the card with your other hand.
9. If the amount of room inside the case is too constricted, you might have to preattach the PCI Express power connectors to the new card.
10. Install the new graphics board, first making sure that no small wires are overhanging the PCI Express slot. If the card seems difficult to push down, check to see whether the connector bracket is sliding in properly.
11. Once the card is firmly in place, replace the connector-bracket screws.
12. Attach the monitor cable. If you've been using a VGA cable, and your monitor has a digital input (DVI, HDMI, or DisplayPort), now is a good opportunity to switch to digital inputs with the right cable.
All done! Organizing cables makes it easier to access the PC's insides later.
13. Double-check to confirm that the graphics card's power connectors are in place. Additionally, verify that no small wires or cables will interfere with any of the cooling fans.
14. Power up the PC. If you hear any rattling, it indicates that something is rubbing against the fans; power down and check to make sure that no fans have become blocked.
15. Once the system is powered up and running normally, install the latest drivers for the graphics card. One more reboot, and you're good to go.