While in general I agree that a new graphics card is the best way to go, and I myself also fully comply with the "upgrade until you can't upgrade no more" theory of PC handling, there's something he needs to look into before he does that:
It's a Dell.
For those who are familiar with this brand then you will know what i'm getting at straight away, for those who aren't:
Unless it's an Alienware branded Dell PC then there's a high chance upgrading will be a lot more complicated than just slapping a new graphics card into it. Dell are notorious with their standard desktops for cutting corners by putting the bare minimum of components needed to run into the case.
The most predominant of these would be the PSU, generally a Dell PC will only have a PSU powerful enough to barely run the components in the machine including the graphics card, this usually means it will be in the region of 200w to 300w (i've actually seen a low end Dell with a 100w PSU) which means that you have a very small range of graphics cards to choose from unless you want to change the PSU, which in itself can be a pain in the butt too because Dell don't always use standard sized ATX PSU's, which means you have to source a specific sized PSU which will no doubt cost twice as much as a standard one.
On top of that, a lot of the standard Dell machines have small to medium form factor cases, which means there's not always a lot of room inside, meaning even if he has the PSU power, he may not be able to physically fit the card in side the case.
When I figure in Dells past record with exploding power supplies, and soldered in components, I personally wouldn't even attempt to upgrade a Dell (heck I wouldn't even own one in the first place, but that's just personal opinion), if you have the money then I would recommend buying a new PC form somewhere that builds them to your specifications, i'd also recommend this course of action for most branded PC's including companies such as HP and the like, as they're generally mass produced, using low end generic components, and are built to the bare minimum to run that specification and need a little more effort and money to upgrade than a custom PC would.
I'm not sure on TGC's policy about linking "shops" on the forum here, but if you're in the UK and want a recommendation for a very good custom PC company that I have been using for +10yrs with no issues and great quality work then send me a PM (they also do custom laptops if that's what you want).
i7, NV960 4GB, 16GB memory, 2x 4TB Hybrid, Win10.
i5 , AMD 6770 1GB, 8GB memory, 512GB Generic SATAIII + 2TB Seagate Baracuda SATAIII, Win7.
i3, Radeon integrated graphics, 4GB memory, 512gB Generic SATAII, Win8.1.
Q6600, Intel integrated graphics, 2GB memory, 180GB Generic SATAII, WinXP.