Here is how to update your name servers at 1and1.com. Tutorial assumes you have a domain name registered through 1and1.com, and starts from their home page.
Now let's learn how to update our domain name's Name server settings
Click "Login" to sign in to your account.
Enter your domain name and password, then click Login.
Then click the "Manage Domain" button.
Click the "Edit DNS Settings" link.
Under "Name Server Settings", select to use "Other name servers".
Enter your new name server settings.
Click "Save" when finished.
Click "Yes" to confirm.
That's it! The domain name's name servers have been updated.
Please note that it could take up to 24 hours for your new name servers to propagate and be recognized across the internet.