LAN is always better for a PC. In case of Wifi only, please check how many WiFi signals are being used in the area. An android app like Cellular-Z or inSSIDer can help. Choose a transmission band that is either empty or has the weakest signal in you area. Also make sure that the router firmware is up to date. You may also have to fiddle around with the Hardware Settings under Device Manager to see the Advanced and Power Management settings. This should be a good starting point.