To update your domain's Nameservers to a third party host, please follow these steps:

Step 1.
Login to your Rebel account and select Domain Manager.

Step 2.
Click directly on your domain name to access the domain editing page.

Step 3.
To the right of the word Manage, select the DNS tab.

Step 4.
In the drop-down beneath Nameserver Information, select Use Third Party Hosting.

Enter your nameservers in the two boxes provided, or update the nameservers you see.

Add extra nameservers by clicking the green +, or remove extra nameservers by clicking the red X. 

Step 5.
Once you are done editing your nameservers, click Save Changes in this section.

Please note, the nameservers will never have a period (.) at the end. If your domain currently has a Classic Hosting, Classic Email or Weebly Website package with Rebel you will first need to cancel the hosting.
For steps to cancel a hosting or email package, visit our article How do I cancel my hosting subscription? 
To cancel a Weebly Website, visit our article How do I cancel my Weebly website?