To change your Wi-Fi password, you'll need to open your router's configuration page, log in using your current details, and change the password under the wireless settings menu. Open your router's configuration page. You can access your router's configuration page through a web browser on a computer connected to your network. If you can't connect via Wi-Fi because you don't know the password, use an Ethernet cable to connect your computer directly to the router.
This will bypass the need for the Wi-Fi password. Enter your router's username and password. Every router will require a username and password before you can access the innards. If you never changed this when you first configured the router, chances are the username is "admin" and the password is "admin" or "password". Of course this varies from model to model, so you should search your model online to see your exact login info. Open the Wireless section.
Once you are logged into your router, you will need to find the Wireless section of the configuration page. The exact name changes from manufacturer to manufacturer, but generally you are looking for a "Wireless" or "Wireless Settings/Setup" tab or button. Change the password. Look for the box labeled "Password", "Passphrase" or "Shared Key". You can enter your new password into this box. Some routers will ask that you type the password again to ensure that you entered it correctly. Check out your security type. There are three main types of wireless encryption: WEP, WPA, and WPA2.
For the most secure network, you should be using WPA2. You may run into issues connecting older devices, however, in which case you could switch to WPA or WPA/WPA2. Selecting WEP is NOT recommended, as WEP encryption is very easy to break (it can take less than 30 minutes to crack a WEP password). Change your network name. While you're here, take a moment to change your network name if you have not already. The name should not include any personally identifiable information, as the name will be publicly broadcast. Changing the name will help deter people from trying to break into it.
Routers with default names are seen as easier hacking targets. Save your settings. Once you are done entering in your new password, click the Apply or Save button. The button's location is different for every router, but is typically located at the top or bottom of the page. The router will take a few moments to process the change, at which point any devices currently connected would be disconnected.