Instructions
Go to your Xbox 360's dashboard and scroll up to find "My Xbox."
Scroll right in the "My Xbox" section to find "System Settings." Press "A" to open the menu.
Open "Network Settings" from the "System Settings" screen.
Open the network configuration menu by selecting "Configure Network" from the "Network Settings" main menu. The "Basic" section of the network configuration menu will open.
Highlight "Wireless Mode," then press "A."
Select "Scan for Networks." Your console will search for Wi-Fi access points for a few seconds.
View the wireless access point results list, then highlight and select the network you wish to connect to.
Enter the network's security key if applicable.