Your default branch is named
master. If you have admin rights over a repository on GitHub, you can change the default branch on the repository.
On GitHub, navigate to the main page of the repository.
In the repository's right sidebar, click Settings.
In the left menu, click Branches.
In the default branch sidebar, choose the new default branch.
You can only switch between branches that already exist on GitHub. To create a new branch through the UI, see "Creating and deleting branches within your repository".