That looks like a Hikvision re-brand NVR with 8 PoE ports and presumably 8 channels, maybe something based on the 7608.
With 8 channels and 8 PoE ports, as you have discovered if you want to use LAN-connected cameras, you can neither add or delete the pre-defined PoE channels.
To use one or more of the pre-defined PoE channels for LAN-connected cameras, you need to select an unused channel and use 'Modify', and change the IP address that is currently in the range 192.168.254.x to be the IP address of the camera that is connected on the LAN.
This is usually best done via the NVR web interface, though should also be possible via the VGA/HDMI interface in your video.
It is very convenient to set the IP address of the LAN-connected cameras to a fixed IP address that matches your LAN addressing using the Hikvision SADP tool. Then you will know what to configure in the NVR.
Download SADP from here if you don't alread have it - it's a very useful tool. :
Hangzhou Hikvision Digital Technology Co. Ltd.