You can rename any file in your repositories directly in GitHub.
Tip: If you try to rename a file in a repository that you don’t have access to, we will fork the project to your user account and help you send a pull request to the original repository after you commit your change.
Browse to the file in your repository that you want to rename.
At the top of the file, click Edit to open the in-browser file editor.
Above the editor, there's a filename field containing the current name of your file. Use this to change the name of the file to the new filename you want. You can also update the contents of your file at the same time, if you so desire.
Enter a commit message describing your change, and click Commit to commit the change to the repository.
Renaming a file also gives you the opportunity to move the file to a new location.