Try the tin-foil hack
What’s been considered an urban legend in most tech circles has become a credible formality amongst DIY geeks. Aluminum foil can actually help boost your router's strength. Create a reflector using tin foil you've got laying around in the kitchen, or use a beer or soda can. It will help increase your Wi-Fi signal and make it more directional.
Kick freeloaders off your Wi-Fi...
If the occasional trip to Starbucks has taught us anything, it’s that sharing the same Wi-Fi with egregious freeloaders completely sucks. If you've got a similar situation at home and want to boot the crowd sucking up all your bandwidth, consider manually adjusting the broadcast channel on the router.
To do it, access the router’s interface by typing the gateway IP address into your browser window. The most popular router manufacturers, Cisco/Linksys, share a default gateway of 192.168.1.1 but here's a full list of common routers and addresses. Then enter the username/password. Nine out of 10 times the username remains Admin and the password is either "password," your router's serial number, or just blank. This all depends on your setup.
Then go to Change the Channel > Wireless > Basic Wireless Settings > Channel to select one that is completely traffic-free.
... and keep them off
If neighbors keep leeching off your open connection and slowing you down, step up your security game. Log into the settings again, go to Wireless > Wireless Security > Channel. From there, select the strongest security mode (WPA2/WPA Mixed Mode) and an encrypted password. You know, something with alphanumeric characters (upper/lower case, punctuation marks, and symbols).