If the cameras are of the same ENS series, firmware updates can be conducted through the NVR using two different methods.
Home --> Camera
Camera --> IP Camera. Hover over camera and click on circle with arrow

.
Click Yes.
Click on Check for Update. Once it finds an update, click on Quick Upgrade.
Click Yes.
Option B:
Home--> Maintenance
Upgrade --> Camera Upgrade
Check for Update --> Quick Upgrade
Click Yes.
Click Yes.