Instructions
Turn on the Nintendo DSi and open the System Settings by clicking the wrench icon.
Scroll to the third page to the right and select "Internet." Select "Connection Settings." Click "None" for Connection 1. Choose "Clear Settings" if you don't see "Connection 1."
Click on "Search for an Access Point." Wait for the Nintendo DSi to search for the local wireless networks. Look at the available connections and select the appropriate one. Click on the lock icon to save the connection and settings changes.