If you purchased your domain from us we can do this at no cost. Simply submit a support ticket and we will take care of it.
If you didn't purchase your domain from us, we are not able to change the DNS since we don't have control over the domain.
Please contact the place you bought it from and provide them with the name servers in your welcome email and they should be able to make the changes for you.
From most ICANN Approved registrars, you can do this yourself using the company's control panel.