The problem you have is that both these computers are laptops which have highly integrated construction totally unlike a desktop in a standard tower. If I want to change a graphics card all I have to do is take off the side and unplug one and replace it - laptops just don't work like that !
It is very likely that the graphics components in both these computers are physically part of the mobo, you would need detailed information to verify that, but that is the normal situation. They use different processors, one an i3 and the other an i5. Basically with a laptop you are stuck with the specification it had when you bought it.
You could try downloading the respective manuals for them from the Dell website and see what possibilities they offer.