When connecting to a WiFi network, Windows will always favor the strongest one available. If you’re in range of several known WiFi networks, Windows will favor the one with the strongest signal strength and not the one that’s faster or has fewer devices connected to it. Regardless of how strong a WiFi signal is, an Ethernet cable connection is almost always going to be better and Windows will favor it over WiFI connections in most cases. However, if your system refuses to favor the Ethernet connection over your WiFi network you can tell Windows to disable the connection altogether when it detects an Ethernet connection. Here’s how.
Right-click the WiFi icon in the system tray and select Open Network and Sharing Center. It’s a Control Panel setting that you can navigate to from inside the Control Panel app and this is just the quickest way of getting to it. The current WiFi network you’re connected to will show up here. Click the connection’s name as highlighted below to go to its properties.
This works on Windows 7/8/8.1/10. It was tested out on both Windows 7 and a preview build of Windows 10.