In the OnePoundEmail portal, you can change the nameservers for a domain by following these steps:

1. Log in to your OnePoundEmail account.
2. Go to the "Domains" section in the main navigation menu.
3. Find the domain you want to change the nameservers for and click on it.
4. Click on the "Nameservers" tab.
5. Enter the new nameservers in the fields provided.
6. Click on the "Save Changes" button.

Please note that the changes made to the nameservers might take up to 24-48 hours to propagate fully.