Welcome to the Community and thank you for posting.
I am sorry to hear you are having issues with your neighbour connecting to your service, this must be concerning.
For information on how to change your WiFi password please see here.
If you have any questions, please do get back in touch.
I've gone to the web address (http://192.168.0.1) to change my password however it keeps saying that my password is incorrect. I have used the 8-digit numbered Settings Password from the router, not the WiFi password (I also tried this just in case). How can I access my settings to change my password? I believe someone may have connected to one of my home internet devices and I wish to change my password asap.