how do I zoom on the camera for iphone 6?

My zoom function while recording video seems to have been restricted with the latest updates. It used to zoom much further than it does now. I was at a small venue concert recently on the 10th row and tried to zoom in to the performer and it didn't get close at all. The tightest I got was a head-to-toe shot with lots of headroom. I couldn't have been more than 45 feet away. That doesn't seem right.

The same way you did on any other model. Two fingers on the screen and spread them. But note that the iPhone does not have optical zoom, only digital zoom, which is a hoax perpetrated on those inexperienced with digital photography. All it does is use less of the sensor, so the resolution is reduced. You are better off always shooting unzoomed, then cropping the picture later. This produces the same end result, but gives you much more control over the finished product.

Does the iphone have internal software for doing this ........ "cropping" the photos ?

Yes, the editing software in the Photos app on the phone supports cropping.