1. Open the repository's page on your GitHub Enterprise instance.
  2. Click Settings. Settings tab
  3. Click Make public. Make Public button
  4. Read the warnings.
  5. Type the name of the repository that you want to make public.
  6. Click I understand, make this repository public. Warning Popup

Warning: When a private repository is made public, its private forks are detached.

For more information, see "What happens to forks when a repository is deleted or changes visibility?".