Depending on if the cameras are on the gateways lan or customer lan you must first determine the IP address of the cameras.
If the cameras are on the gateways Lan then you will have to add your laptop to that network. You can determine the IP address from the gateway manager by going to the ping from gateway option and clicking on the camera needing the update. Once you have determined the IP and that you can communicate to it from the network your Laptop or PC is a part of you can use the update tool to update. Below is a link to the update tool.
http://files.clear2there.com/onvif_ip/FW_v1.8_Update_Tool.zip
With this tool you can browse to the firmware upgrade file "v1.8.0601.1001.25.0.46.2.32_20150716"
You can update a range of cameras all at once if you need as well by changing the IP range.