How to change focus point during a video?

I'm a bit new to photography, & this has been bugging me since I first got my camera.
I have a Nikon D5100, great investment. When I take a picture I change the focus point by moving it with the navigation button, but if I did it during a video it would take a while. Which obviously will make it look funny when your watching it. So I'm asking, is there any other way to change the focus point besides the method i'm using? If so how?
Heres a example of how I'd like the videos to come out:

Set the lens to manual focus.
Then while you're shooting video, turn that rubberized ring on the lens -- the focus ring.
That changes the focus.

I'm teasing a little, but only a little -- don't use AF while shooting video, focus manually.

Manually focus your lens. Eventually you'll want CIne lenses which focus smoother and have more throw which allows the lens to focus more gradually. Your lens may focus from 5'-15' by moving the barrel of the lens 1/4 inch while on a cine lens you need to move it a much longer distance. Look at Cooke lenses and you'll see cinema lenses. The are painfully expensive but on the site you will see the difference between those lenses and the ones on your camera.