Changing your DNS is quite easy. Here's how to do it:

1. Visit http://www.idomainsmadesimple.com

2. login using your username and password

3. Click on the domain you want to edit

4. Click the modify DNS button

5. Enter you new DNS details Under "Name" then click the "Add" button. Is usually looks something like this ns1.somedomain.com

6. Repeat the process for the secondary name server, this one usually looks something like the: ns2.somedomain.com

7. Next delete you OLD nameservers (if you have any)

That's it! you've updated your DNS details.