See that “Edit this page” button on the top right? If you want to edit a page just click it.
Clicking that link will open up the page in GitHub, where you can directly edit the page within the web-based file editor. Alternatively, you can clone the repository and make your changes by pushing your local edits. For editing existing pages, the former approach is fine, for adding new pages or making other making significant changes to the site content the latter would be better.
After commiting your changes, you’ll be able to create a new pull request for approval. Once approved, changes will take a few minutes since the site must be rebuilt, deployed on s3 and propogated onto the content distribution network edge servers.
The current status of the build is shown by the badge below. Once the new commit builds properly (changes to passing), changes will take around 5 minues to propogate.