If your NVR is connected via your router/network, all you have to do is to:
1) type the NVR's IP into your browser, when asked, enter your log in credentials (log in name and password)
2) go to the upper right of the screen and click configuration tab
3) lower left side of the screen, click camera management. You should see a list of all the cameras connected to your NVR with their own assigned IP addresses.
4) click on the first camera IP address and another window/tab will appear asking you to log in to the camera. Enter the log in credentials (usually the default log in is Admin and the password is the default 12345). When that camera pops up, you will see "configuration" tab on the upper right again.
5) click configuration and it will take you to the local configuration and advance configuration page.
6) on the right side, click advanced configuration, --> system and click on the maintenance tab on top.
7) on the bottom, you will see "remote upgrade". You will need to press "browse" and locate where you put the firmware (assuming you have already downloaded it and placed it where you can easily find it...like on your desktop) and choose the file.
8) click "upgrade" and the upgrade process will begin.
You will have to do this for each camera by repeating steps 4-8 but instead, you will choose the next camera on the list on step 4).
I think there is another easier way of upgrading all the cameras at once by "batch upgrading" but I am not familiar how to do this.
Maybe someone familiar with batch upgrading can chime in and post instructions on how to do this?
I hope this helps.