To configure your network to use WPA security, you must first change your router's settings, and then you must configure the network adapter for each of the computers on the network.
Access Wireless Settings
Log on to your router as the administrator using your web browser; type the URL for your router in the browser's Address box and then provide the login name and password for the router when prompted for this information. You can find the URL for your router in the documentation that came with your router. Alternatively, go to the router manufacturer's website, download the documentation, and consult it for the URL and the default login name and password.
From the main configuration page for your WiFi router, click the Wireless Settings link or similar command. This opens the configuration page for the router's security settings such as WEP and WPA.
Click the WPA-PSK (Wi-Fi Protected Access Pre-Shared Key) option button in the Security Options portion of the Wireless Settings page (or similar page on your router's configuration website).
WPA creates the shared keys automatically and cycles through them at a specified interval. You configure WiFi adapters and other devices on your network for WPA using the same passphrase you specify when you configure the WiFi router. The use of the passphrase is consistent among all WiFi routers in terms of the WPA configuration. You don't even see the keys that are generated, so you have to use a passphrase to configure your WiFi adapters.
Type a passphrase (from 8 to 63 characters). If you want to change the default interval for the key lifetime, click in the Key Lifetime text box and type a new value (in minutes). The shorter the key lifetime, the more secure the WiFi network. The default for most routers is a 60-minute key lifetime. Because your WiFi network probably isn't going to be the target of a host of WiFi miscreants (you are a small fish in the sea of WiFi networks), you can leave the key lifetime at its default setting. If it helps you sleep better, reduce the key lifetime to 30 minutes. A shorter lifetime will not affect data flow on the network negatively, but it will take a hacker more than an hour to decipher a shared key (and then that key will be changed, anyhow).
After selecting the settings for WPA security, click Apply (or a similar command on your router) to save the new security settings as part of the router's configuration.
Set Advanced Security (WPA) for a WiFi Adapter
After you have configured your router to use WPA security, you must configure the WiFi adapters on each of the network computers for WPA. On one of the computers in your network, open the configuration software for the WiFi adapter (right-click the WiFi adapter's icon in the system tray and select Open from the context menu). To set advanced security for the WiFi adapter, select the Advanced option button and then click the Advanced Security button. The Advanced Security dialog box opens.
Enter Passphrase and Apply New Settings
Enter the passphrase you specified in step 3 for the router in the Advanced Security dialog box (or similar dialog box using your adapter's configuration software; for example, if you are using the Windows Wireless Networking Properties dialog box for your adapter, the passphrase is entered on the Association tab). Click OK. Back in the main configuration screen for the WiFi adapter, you can then apply the new settings to the adapter by clicking Apply.