Please follow the instructions below to turn off WiFi on your D-Link router:
Step 1: Open your Internet browser and type the IP address of the router in the address bar. The default IP address is 192.168.0.1. At the login, enter the username (admin) and your password (default password is blank).
Step 2: Click on the Setup tab at the top and then click Wireless Settings on the left side.
Step 3: Scroll down to the bottom of the page and Click Manual Wireless Network Setup
Step 4: Uncheck the Enable Wireless Option and Click Save Settings
Please Note-- If your router is Dual Band, you need to disable both the 2.4Ghz and 5Ghz wireless bands.