You can edit files directly on GitHub in any of your repositories using the Ace editor.

Tip: If a repository has any protected branches, you can't edit or upload files in the protected branch using the web interface.

  1. In your repository, browse to the file you want to edit.
  2. In the upper right corner of the file view, click to open the file editor. Edit file button
  3. On the Edit file tab , make any changes you need to the file. New content in file
  4. Above the new content, click Preview changes. File preview button

  5. At the bottom of the page, type a short, meaningful commit message that describes the change you made to the file. Commit message for your change

  6. Below the commit message fields, decide whether to add your commit to the current branch or to a new branch. If your current branch is master, you should choose to create a new branch for your commit and then create a pull request. Commit branch options

  7. Click Propose file change. Propose file change button

Further reading