Before choosing a upgraded graphics card, consider what the card's power requirements are. In some/most cases, older computers will have to buy a more powerful power supply. That said, Windows 8.1 requires a minimum of a AMD HD5xxx series to meet the minimum requirements. With the existing processor in your son's computer, you don't need a really powerful card. The R series are the latest AMD offerings, any of which will offer better performance and allow for future upgrades to the rest of the system. Check Newegg or Tiger Direct for pricing and system requirements.