Here are the steps that you need to do to switch the account.
1. From the Wii home screen click on round “Wii” (Options) button in bottom left corner
2. Click “Data Management”
3. Click “Save Data”
4. Click “Wii”
5. Find “Netflix Channel” (red square with letter N), click on it, select “Erase” and then confirm “Yes”
6. Try to find more “Netflix Channel” icons in that area, scroll to next screen if required (there could be more than one saved block)
7. Return to Wii menu and start Netflix Channel. You should get “Are you a Netflix member?” question and when you answer “Yes” it will show you activation code, which you can use at netflix.com/activate.