All very helpful, folks! I'm not tech savvy when it comes to video cards; the specs seem daunting to understand. The machine has an NVidia GeForce GT620 as a video card--and I'm not actually sure it IS on the motherboard. (But I think it likely.) So, I'm pretty much a newbie when it comes to video cards. But I'd done a little research and that said that a desktop card rather than a gaming card would be better for 3D rendering--thought it did say the desktop cards are pricey.
Looks like what you've given me so far is a very good start!