To edit the content, go into the _sections folder, here direct link:
https://github.com/si17/si17.github.io/tree/master/_sections
click on any of the files, login with your Github account, edit, the syntax is Markdown, if you need details on how to create something specific, see example here:
https://guides.github.com/features/mastering-markdown/
Then wait 5 minutes to see the updates on the website (do shift+refresh if you still don’t see them in your browser to do a forced refresh).