backup/download via network connection

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Hi,

I have this DVR http://www.ebay.com/itm/4CH-4-CHANNELS-Home-Video-Surveillance-CCTV-DVR-Security-System-4-Outdoor-Camera-/160718153946

I want to backup the files to a large ext. drive since the usb connection is limited to small size/partition. I connected and configured the DVR network setting and I can access the DVR using the browser. The manual stated that there is option to download/backup files via network connection but I don't see any option to do this when accessing remotely using either the browser or remote client software. I have been trying and can't find any information on how to do this. Anyone has any idea please help. Thanks.