Hi,
in Device Manager there is no WiFi network adapter, so you can only connect to the internet via a network cable.
Do the disconnections also occur during normal web browsing? Is the PC's network cable connected directly to the router's LAN port or via the ethernet wall socket?
Go to Device Manager,expand network adapters,right click on your network adapter,Realtek PCIe GbE Family Controller>Properties,then click on Power Management tab**,uncheck** the checkbox:"Allow the computer to turn off this device to save power ". Click on the Advanced tab and disable any options regarding energy saving: Energy Efficient Ethernet(EEE), Green Ethernet, Power Saving Mode etc.
See if the situation improves or if the problem still persists.