Instructions
Remove any DS game that may be in the DSi XL, then turn the DSi on. Wait for the main menu to appear.
Tap on the "System Settings" icon on the main menu.
Tap on the "Internet" button, located on the third page of the system settings.
Tap "Connection Settings" to open the wireless network settings.
Tap on a connection box that says "None" on it, then tap "Search for an Access Point" in the menu that appears.
Tap on the network you want to connect from the list that appears.