Step 1
Log in to your 1&1 Control Panel and select the relevant package.
Step 2
Click on Domains in your control panel 


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Step 3
Select the domain you'd like to change name servers for
 
Step 4
Click "Advanced Settings" 
 
Step 5
 
Select "Edit DNS settings" , then "Other Name servers"
 
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Step 6
  • Enter the first name server address into the Primary name server text box.
  • Select My secondary name server from the Secondary name server drop-down box to add a second address.
  • Enter the second name server address into the 1st secondary name server text box.
  • Click on Save to proceed.
 
Please note:
You may add a third and forth name server address if necessary however only two are required.
 
 
Please note:
All DNS changes may take up to 72 hours to be fully updated and recognised by all servers/computers on the Internet.

 

1&1 Instructions Here

Additonal article:

http://help.1and1.co.uk/domains-c40986/manage-domains-c79879/dns-c43146/change-dns-settings-a617637.html