You can configure that using the "in picture" settings. Look at the live view menu, there should be a button (somewhere next to the whiper and light buttons) activating the ocd menu. Then navigate using the ptz arrows. Here you should be able to activate digital zoom.
The Dahua PTZ´s offer a maximum focal length of 300mm. If you really need more zoom, you could use the Fujifilm SX 800 with up to 800mm focal length and a 1/1.8 - 2mp Sensor. Long Range Surveillance Camera SX Series | Fujifilm [United States]
For PTZ Capabilities, you should use an external...