Welcome to the Community!
There are a few reasons why you may not be able to change the nameservers on a domain. Please access your domain manager to see if any of the following apply.
> The domain is in a whois (ICANN) Veriifcation status (must first have registrant info approved)
>The domain is expired in the account (must be renewed first)
> The domain is in the middle of a Change of Account or a Transfer (must be canceled or completed to change)
> The domain is not registered at GoDaddy, but is DNS only (must be changed at the current registrar)
If none of these apply, please contact our support team so they can review for you.